8
Invertebrates 1: Biological Aspects

8.1 An Introduction to Invertebrate Biology

Invertebrates are metazoan animals that lack a backbone. They include creatures as diverse as mites that are smaller than the nucleus of a large protozoan to giant squid several metres long. From a forensic perspective, the most important invertebrates are those belonging to the phylum Arthropoda and in particular the insects. The arthropods are the most successful invertebrates in terms of their abundance, biomass, and numbers of species. Arthropods are characterised by their possession of a hardened exoskeleton that is shed periodically to accommodate growth and they have specialised jointed appendages. Typical examples are scorpions, crabs, and moths.

The study of insects is ‘entomology’, a word derived from the Greek words entomon (ἔντομον – an insect) and logia (λογία – study of). Logic would therefore suggest that forensic entomology is the use of insects in legal investigations. However, many workers restrict the definition to the use of insects in murder and suspicious death investigations, thereby excluding the numerous other legal cases in which insects are involved. Sometimes, the term ‘medicocriminal entomology’ is used to emphasise this restricted definition. This chapter will cover the basic biology of some of the most forensically important invertebrates and those seeking more detail are advised to consult Gennard (2012) and Rivers and Dahlem (2014).

Insects account for 72% of all known species of animals and together with other terrestrial arthropods they can be found in virtually every terrestrial habitat, both natural and man‐made, from the polar‐regions to the equator. Within these regions, insects, and other arthropods, occupy virtually every conceivable ecological niche. Some are specialist herbivores, carnivores, detritivores, or parasites, whilst others are generalists that consume a variety of foodstuffs. Their lifestyles sometimes bring them into conflict with mankind because they consume the same food as ourselves, use us as their food, or occupy our dwellings. Knowledge of their biology is therefore useful in reducing the harm that certain species cause directly or indirectly (e.g. through spreading diseases) and in understanding how they can provide forensic evidence. However, most arthropods and other invertebrates are harmless to us, many are extremely valuable as food, pollinators of our crops or biological control agents, and they all have an important role in the normal functioning of ecosystems.

8.2 Invertebrates as Forensic Indicators in Cases of Murder or Suspicious Death

The invertebrate species that provide forensic evidence in cases of murder or suspicious death investigations can be grouped into those that are attracted to dead bodies, those that leave dead bodies, and those that become accidentally associated with the dead body and/or the crime scene.

8.2.1 Invertebrates Attracted to Dead Bodies

Numerous invertebrate species are attracted to dead bodies, including detritivores that feed on the decaying tissues, carnivores and parasitoids that come to prey on the detritivores, and coprophages that tend to feed on faeces rather than the decaying tissues of the dead body (Table 8.1).

Table 8.1 Groups of invertebrates attracted to decaying remains.

Taxon	Common name	Examples	Stage of decay
Diptera	Flies	Calliphora vicina	Fresh, bloat
		Eristalis tenax	Active decay (liquefied)
		Piophila casei	Late decay
		Hermetia illuscens	Drying out
Coleoptera	Beetles	Nicrophorus vespillo	Fresh
Coleoptera	Beetles	Nitidula carnaria	Dry
Hymenoptera	Ants, bees and wasps	Vespula germanica	Fresh and dry
Hymenoptera	Ants, bees and wasps	Solenopsis spp.	Fresh and dry
Lepidoptera	Moths and butterflies	Tinea pellionella	Dry
Blattidae	Cockroaches	Periplatena americana	Fresh and dry
Termitoidea	Termites	Amitermes lunae	Dry
Acari	Mites	Myianoetus muscarum	Fresh
Dermaptera	Earwigs	Forficula auricularia	Probably dry but few observations
Diplopoda	Millipedes		Probably dry but few observations
Mollusca	Slugs and snails	Arion ater	Fresh to dry

8.2.1.1 Detritivores

Detritivores, also referred to as ‘decomposers’ and ‘saprophages’, are creatures that consume dead organic material. As in life, after death, animal and plant tissues present different physical and chemical challenges and nutritional rewards. Therefore, they tend to be exploited by different guilds of detritivores. In addition, some detritivores are specialists that feed solely on dead organic material but many also consume other foods, depending upon circumstances. Even invertebrates that we normally consider predators (e.g. social wasps) often consume dead organic matter.

A dead body represents a temporary source of easily metabolised organic matter that, unlike that of living organisms, is chemically and physically unprotected. In the initial stages, it therefore attracts highly mobile r‐type species that are adapted for finding and exploiting such temporary food sources: r‐type species are typified by short life cycles and the ability to undergo explosive increases in population under the right conditions. They rapidly consume the easily degradable tissues until all that remains is material that does not have sufficient nutritive value to support their growth. Therefore, with time, r‐type detritivore species are replaced by k‐type species with longer life cycles and lower reproductive rates that are capable of exploiting food that is difficult to metabolise and has a lower nutritive value.

The most important detritivores, from a forensic perspective, are those belonging to the insect order Diptera – the true flies – and most of them arrive during the early stages of decay. Many beetle (Coleoptera) species are also useful as forensic indicators and these are mostly species that arrive when the body is drying out. Certain ant and social wasp species (Hymenoptera) can rapidly remove large amounts of soft tissue from a dead body, but they will be dealt with among the heading ‘predators and parasitoids’. Many other groups of invertebrate are associated with dead bodies. However, they are only mentioned in passing in the forensic literature or in relation to specific cases. Nevertheless, it is essential to take account of their presence and appreciate how they influence decay.

8.2.1.1.1 Diptera (Flies)

Flies (Order Diptera) are the most important forensic indicators, especially for the determination of the post‐mortem interval (PMI). Blowflies, fleshflies, phorid flies, and muscid flies are among the first insects to colonise a body, whilst piophilids, stratiomyids, and trichocerids tend to arrive later in the decay process. The term ‘maggot’ is commonly used when referring to fly larvae and to the larvae of other insects if they are white and worm‐like in appearance. However, in the past, ‘maggot’ was used to denote a ‘whimsical or eccentric idea’. For example, in 1738 it was said of the composer George Frideric Handel that ‘Mr Handel's head is more full of maggots than ever’. Whilst the meaning might have changed, maggots are certainly inspirational and a source of both fascination and forensic evidence.

Adult Diptera are easily distinguished from other insects because they possess only one pair of wings and this is referred to in their name: ‘Diptera’ is derived from the Greek δι (‘di’) meaning ‘two’ and πτερόν (‘pteron’) meaning a wing. In all other winged insects, apart from the rare parasitic stylopids, the adults have two pairs of wings. In adult Diptera, the rear wings have evolved into structures called halteres that act like gyroscopes and contribute to the remarkable aerobatics that many fly species perform. All flies exhibit complete metamorphosis (i.e. holometabolous development) in which an egg hatches to give rise to a larval stage that goes through a number of moults before pupating to become a fly.

The Diptera are divided into three sub‐orders: the Nematocera, Brachycera, and Cyclorrhapha (Table 8.2). The Cyclorrhapha includes most of the species of forensic importance. The name derives from the Greek for ‘circular seam’ and refers to a line of weakness encircling the puparium close to the anterior end. When the adult fly is ready to emerge, it inflates a bag‐like structure called the ptilinum on its head: the inflated ptilinum pushes against the puparium that promptly splits open at the seam and thereby allows the adult insect to escape. The ptilinum then deflates and returns behind the ptilinum suture, never to be used again.

Table 8.2 Taxonomy of the order Diptera.

Sub‐order	Adult	Larva	Pupa	Forensic example
Nematocera	Long, thin body; many‐jointed antennae; often long thin legs	Well‐developed head capsule; mandibles bite horizontally	Obtect (wings and limbs glued close to the body). May or may not form a cocoon	Trichocerid flies (Winter gnats, e.g. Trichocera saltator)
Brachycera	Body often thick and stout; antennae with few segments; legs not modified	Poorly‐developed head capsule; mandibles bite vertically	Exarate (wings and limbs not glued close to the body). May or may not form a cocoon	Stratiomyid flies (Soldier flies, e.g. Hermetia illuscens)
Cyclorrhapha	Body short and stout; 3‐segmented antennae with feathery arista on the 3rd segment; legs not modified	No head capsule; body bullet‐shaped; mouth hooks drag food into the oral cavity	Coarctate (the last larval cuticle is retained to form a protective ‘puparium’)	Calliphorid flies (e.g. Blowflies, flesh flies, muscid flies, phorid flies, syrphid flies, piophilid flies)

Calliphorid Flies (Blowflies)

The family Calliphoridae includes over 1100 species but from a forensic perspective, it is the subfamilies Calliphorinae and Lucilinae that are the most important. These are stoutly built insects with shiny blue, black, or green bodies that are commonly known as ‘blowflies’. One explanation for the term ‘blowfly’ is that it derives from the noun ‘blow’, which means a mass of fly eggs. Meat, a wound, or a corpse covered in fly eggs is therefore said to be ‘fly‐blown’ and the insect responsible is a ‘blowfly’. Another commonly cited explanation is that it was once believed that flies blew their eggs onto meat in a similar manner to a child using a peashooter. In the UK they are referred to as ‘greenbottles’ or ‘bluebottles’, but because many flies look superficially similar it is better to use taxonomic terms. The larvae of many blowfly species are detritivores and the female flies arrive to lay their eggs within minutes of an animal dying. The sub‐family Chrysomyinae are commonly known as screwworm flies and the adults' metallic green coloration gives them a superficial resemblance to the Lucilinae. The larvae of several Chrysomyinae are notorious parasites of vertebrates (including humans), but some are also detritivores and provide forensic evidence in the same way as blowflies.

There are hundreds of species of blowfly and a corpse is often exploited by several species at the same time. However, not all blowfly species utilise corpses and a dead body may be colonised by the larvae of many different species of Diptera other than those belonging to the Calliphoridae.

Blowfly Life Cycle

The life cycle of ‘typical’ blowfly species, such as those found on dead bodies, is straightforward. The gravid female fly (i.e. one ready to oviposit) lays her eggs on the corpse. She usually chooses one of the natural openings, such as the nose, ears and mouth, the eyes, or the site of a wound (Figure 8.1). Blowflies are attracted by the odour of blood and species such as Calliphora vicina and Lucilia sericata will lay eggs on the wounds of an injured animal before it dies. If they are accessible, eggs may also be laid in the anus and genitalia as well as the vegetation underneath a corpse. Blowflies will lay eggs through the zips of suitcases when these contain a body or body parts.

**Figure 8.1** Blowflies ovipositing within and around the nasal cavity of a sheep. The flies began laying eggs within 5 minutes of the animal being killed.

Blowflies colonise corpses that are fresh or at the early stages of decay, and although the adult flies may feed on a body that is dried out or skeletonised, they would not normally lay their eggs upon it. Even if the window is open, the colonisation of bodies that are indoors is often delayed and the blowfly species composition is reduced (Reibe and Madea 2010). Adult blowflies are usually only active during daylight hours, although the temperature must be high enough to permit flight. There is uncertainty concerning whether blowflies lay eggs at night or under low‐light conditions. However, Wooldridge et al. (2007) found that Calliphora vomitoria and L. sericata have a limited ability to locate corpses during the hours of darkness. By contrast, Wyss and Cherix (2004) reported that adult C. vicina located human remains that were 10 m inside a cave, laid eggs upon it, and these hatched to give rise to developing larvae. At this point there was total darkness and the ambient temperature was a constant 5 °C. The unwillingness of blowflies to lay eggs at night may therefore be associated with their natural cycles of activity rather than an inability to navigate when it is dark.

Blowfly eggs are laid in batches that can number up to 180 and a female fly may lay several thousand eggs over the course of her life (Figure 8.2). When an egg hatches, a first instar larva emerges. At this stage, it is small and delicate and it moves to where it can find optimum conditions – not too damp and not too dry. Blowfly larvae feed using chitinous mouth‐hooks that drag material into their oral cavity (Figure 8.3). They consume both the tissues of the corpse and the microbes that grow on it. In addition to the physical act of feeding, maggots also release enzymes and other substances that help to break down the underlying substrate. After approximately 24–48 hours, the larva moults to the second instar and after a further 24–48 hours, it moults to the third instar. The third instar larva (Figure 8.6a) feeds voraciously and rapidly increases in size and weight over three to four days. Development times are strongly influenced by temperature and some blowfly species develop quicker than others do. Blowfly larvae tend to develop fastest when reared in groups and their development rate increases with larval density. This is probably owing to improved feeding efficiency from the combined effects of their digestive secretions and the heat generated when large numbers of second and third instar larvae are congregated together.

**Figure 8.2** Blowfly eggs laid upon vegetation underneath a body. Although the eggs are normally laid on the body, they are sometimes laid in protected locations nearby.

**Figure 8.3** Anterior of the third instar larva of the blowfly *Calliphora vomitoria*. The cephalopharyngeal skeleton has a large surface area for the attachment of muscles, thereby allowing the mouth hooks to be dragged forcefully back and forth.

Laboratory experiments show that the development of blowfly larvae is affected by the nature of the tissues they are reared on (e.g. muscle, liver, kidney, or brain). However, the larvae tend to wander rather than staying in a fixed position during their development, so most of them probably consume a variety of tissue types. Blowflies may not gain immediate access to a dead body for all sorts of reasons and even as little as seven days decomposition can cause a marked decline in growth rate of C. vicina larvae (Richards et al. 2013). These factors could be important considerations when calculating the minimum time since death. Although blowfly larvae develop faster when feeding communally, very high population densities result in excessive competition. This reduces feeding efficiency and may even result in starvation. This delays development and causes a reduction in larval size. If the third instar larvae cannot reach a minimum size, they die without pupariating. This is another important consideration when calculating the PMI. However, a fresh, whole, human body presents blowfly larvae with more than enough food for at least the first generation to complete their development. Separated body parts, such as hands, are a more limited food resource, especially if the maggot population is high.

In many blowfly species, competition does not induce cannibalism, although most experiments have been done with groups of related individuals of the same age. Whether third instar larvae would consume first instar larvae, especially if they were unrelated, is not known. However, the larvae of some Chrysomyinae are well known for their willingness to behave as cannibals/facultative predators of their own and other species of maggot, even if there is no shortage of dead tissue available to them. One of the best‐known examples of this is Chrysomya albiceps, whose second and third instar larvae are aggressive competitors of other maggots. Although this is among the first species to colonise a dead body, if it arrives shortly after other species, it might then kill off its competitors. Therefore, the presence of Ch. albiceps and other predatory insects means that caution is needed when interpreting minimum time since death calculations. Ch. albiceps is common in parts of Africa, Asia, South America, southern and central Europe, and recorded as far north as Belgium. However, it has not yet established itself in the UK.

Once a third instar blowfly larva has developed sufficiently, it empties its gut and (usually) leaves the corpse in search of somewhere to pupariate (Figure 8.6c). This normally takes place at night when they are less vulnerable to predation and desiccation. These larvae can be distinguished from those that are actively feeding, because their gut is clear rather than dark – this can be useful in determining the age of a larva. The larvae of species such as L. sericata and C. vicina travel several metres from the corpse before burrowing into the soil and pupariating. By contrast, some species, such as Protophormia terraenovae, may pupariate on the body or its clothing.

In countries with cold or temperate climates, some blowfly species (e.g. C. vicina) overwinter as diapausing post‐feeding larvae within the soil and pupariation takes place once the soil temperature rises in the spring. When a larva begins to pupariate, its body contracts and after moulting, the third instar cuticle is retained to form a protective puparium surrounding the pupa. We therefore refer to this stage of the life cycle as ‘pupariation’ – the formation of a puparium. The time taken for a pupa to develop into an adult fly, like all the other stages, is temperature dependent and may last from just a few days to weeks.

After the adults emerge, they fly off in search of food. In addition to carrion, adult blowflies also feed on nectar (they are allegedly more efficient pollinators than honeybees of cabbages and onions), honeydew, dung, rotting fruit, and other decomposing matter. Blowflies are strong fliers and this flight is primarily fuelled from the glycolytic breakdown of carbohydrates – principally from the glycogen reserves in the fat body. They are therefore not capable of the long sustained flight of migratory insects such as locusts and some moths and butterflies, which use lipid as their main flight fuel. Nevertheless, over time they may disperse considerable distances through a combination of directed and random flights. For example, in South Africa, Ch. albiceps were recovered up to 37.5 km from their release site after 7 days (Braack and Retief 1986), although the movements of L. sericata in the UK appear to be much more modest in comparison (Smith and Wall 1988).

In many blowfly species, the female flies need a protein meal before they can lay their eggs. Some male blowflies (e.g. Phormia regina) also require a protein meal if they are to mature their sperm, but it is uncertain whether this is the case for the majority of species. It is said that female blowflies typically only mate once (this is unusual in all animals), although the male may mate many times (Erzinçlioğlu 1996). Davies (2006) found that under field caged conditions only 20% of female C. vicina had laid any eggs by 32 days after emergence. He found that there was a similar but not so pronounced delay in oviposition by adult L. sericata and for both species their fecundity was highly variable and generally less than expected from the temperature the flies experienced. The adult lifespan varies between species and can be from a few weeks to several months. Most adult lifespan studies involve laboratory‐reared insects and this results in overestimates, since in the wild the majority of flies die from predation, starvation, and disease before reaching their maximum potential age. In some species (e.g. P. regina), adult flies enter diapause overwinter during which they seek shelter (e.g. house lofts), reduce their feeding, and do not mate. In this instance, the adult lifespan will be prolonged.

Fleshflies (Sarcophagidae)

Adult fleshflies are usually greyish in colour with three longitudinal dark stripes on their thorax, a tessellated pattern on the upper abdomen, and they often have bright red eyes, although the red colour fades after death (Figure 8.4a–c). The tarsal claws and the pluvilli (tarsal pads) are usually large and give the fly an appearance of being ‘big‐footed’. As their name indicates, the larvae of many sarcophagids develop on the flesh of dead animals, but the family also includes examples of general scavengers, parasites, parasitoids, and predators. In Europe, Sarcophaga argyrostoma is the sarcophagid species most commonly recovered from human corpses (Szpila et al. 2015).

**Figure 8.4** (a) Adult fleshfly *Sarcophaga carnaria* (Sarcophagidae). Note the large pluvillae (feet), robust body, and grey longitudinal stripes on the thorax. In many species, the eyes are bright red but this fades after death, as in this specimen. Unlike blowflies, the body of fleshflies is never metallic and the abdomen is tessellated, i.e. has a pattern of pattern of black spots on a grey background. Scale = mm. (b) Male sarcophagids often have large complex genitalia and their shapes are used as taxonomic indicators. (c) Unidentified sarcophagid investigating a dead mole.

The eggs hatch in the female fly's reproductive tract and she therefore lays first instar larvae. Adult fleshflies are reportedly more willing to fly during wet weather than blowflies and may, therefore, be among the first to colonise a corpse under these conditions. However, there is little evidence to support this suggestion and there have been few comparative studies on the propensity of flies of forensic importance to fly under different environmental conditions. Some workers state that adult fleshflies are among the first insects to arrive at a corpse, whilst others consider them to delay arrival until after the blowflies have established themselves. There is a report of first instar larvae of Sarcophaga aratrix attacking and killing much bigger C. vicina larvae (Blackith and Blackith 1984). However, it is not known to what extent (if any) other species of sarcophagid larvae commonly found on corpses are predatory. If they are not predatory, they are unlikely to gain any benefit from delaying colonisation until after the blowflies have established a larval population with which they will have to compete. The discrepancy probably results from differences in biology between the various fleshfly species and the individual circumstances (e.g. which species happened to reach the dead body first). Sarcophagid larvae can be distinguished from those of blowflies and other Diptera by their spiracles, which are partially hidden in a deep cavity, but they are otherwise difficult to identify.

Muscid Flies

Muscid flies belong to the family Muscidae, which contains over 5200 species and includes insects that exhibit a wide variety of lifestyles at both the adult and larval stages (Skidmore 1985). The adults are usually small and brown or grey in coloration. The larvae often resemble those of blowflies but in many species they can usually be quickly distinguished by the wavy shape of the slits in their posterior spiracles (Figure 8.5) – the slits of calliphorid larvae are straight (Figure 8.6b).

**Figure 8.5** Posterior spiracles of *Musca domestica* larvae: (a) third instar larva – note the wavy slits – compare these to Figure 8.6b, and (b) second instar larva.

**Figure 8.6** (a) *Calliphora vicina* third instar blowfly larva. The full crop indicates that this larva has not yet finished feeding. (b) Posterior spiracles of third instar larva. (c) Post feeding third instar larva starting to contract. Note the gut is empty.

The genera Muscina and Hydrotaea (Ophyra in older literature) include several species that are occasionally recovered from dead bodies. Nuorteva (1974) describes a case in which Muscina stabulans larvae were reared from a blood‐soaked shirt that had belonged to a man who was stabbed to death. The shirt was removed from the man's body by the assailant and thrown into a rubbish bin 13 days later. On recovery of the shirt, it was found infested with fly larvae and these were reared to adulthood. The adult flies emerged in two waves: the first wave corresponded with eggs laid on the date on which the victim was stabbed and the second wave to when the shirt was thrown into the bin. Two waves of emergence occurred, because the shirt was placed in a plastic bag during the intervening period and this prevented other flies from accessing it.

Phorid Flies (Scuttle Flies)

Phorid flies belong to the family Phoridae – a large group that contains over 2500 species and examples of virtually every life style (Disney 2012). They are all small flies, 1.5–6.0 mm in length, and have a characteristic ‘humped’ profile. The name ‘scuttle fly’ is derived from their rapid running behaviour (Figures 8.7a and b). Because of their small size, phorid flies gain access to containers and rooms that exclude blowflies. The larvae of many species are detritivores and some feed on dead bodies.

**Figure 8.7** (a) Adult phorid flies (note the humped profile) and an empty puparium. Each small square = 1 mm. (b) Phorid larvae do not always move away from their food source to pupariate. These have pupariated on the dead snake they were feeding on.

Case Study: Phorid Flies as Indicators of the Time since Death (Disney et al. 2014 )

The body of a suspected murder victim was discovered at his home in London on 15 November. He was last seen alive on 8 October, but it was uncertain at what point over the intervening period he died. This was calculated by identifying the insect species associated with the body and their life cycle stages and then working out how long it took them to develop from the environmental conditions they experienced. The poorly ventilated room maintained an even temperature of between 12.5 and 16.7 °C. Despite the low temperature, the empty pupariae of C. vicina and those of unidentified muscid and faniid flies indicated that the man was dead for sufficient time for at least one generation to complete development. Of these, C. vicina would have taken the longest to reach adulthood, but this would still have taken ‘only’ about 29 days and the man had been missing 38 days. The date of the initial infestation was therefore uncertain. Fortunately, three species of phorid fly were also found, including the empty pupariae and adults of Megaselia abdita and Megaselia rufipes and a recently emerged female Dohrniphora cornuta. Calculations based on the development rates of the phorid flies suggested that the man had been dead for 36–39 days – which was in keeping with the time that the man disappeared. This case indicates that phorid flies may colonise a corpse shortly after death and that they can sometimes prove more useful than blowflies in determining the PMI. Phorid flies are particularly likely to colonise a fresh dead body in indoor situations. This is probably because they can establish a population in the absence of (or with reduced) competition from blowflies and other insects.

Megaselia scalaris is another cosmopolitan phorid fly that is frequently found on dead bodies, both above and below ground. It will also infect wounds of living animals, including humans. Me. scalaris is an unusually adaptable insect and its larvae feed on everything from shoe polish to other insects. Indeed, it is allegedly able to undergo several generations within the intestine of living humans. Cases of so‐called ‘intestinal myiasis’ are reported for several other species of Diptera, but the evidence is seldom convincing. Most instances probably relate to poor personal hygiene resulting in infestations in the perineal region, larvae consumed with the food and ultimately defecated, and infestations of faeces after defecation. Unless they are parasites specifically adapted for living within the intestine of their host (e.g. Gasterophilus intestinalis), Diptera larvae lack the means to grasp onto the intestinal wall (and thereby avoid being expelled by peristaltic contractions) or to survive permanently submerged in fluid. Me. scalaris is found in many parts of the world although it is mostly associated with warm climates. It has been introduced into the UK but has to overwinter indoors. A number of other phorid flies are also found on corpses, including Diplonerva florescens, Me. abdita, Me. rufipes, and Triphleba hyalinata. They all tend to be found during the later stages of decay as the body is starting to dry out, although they may also colonise a body at earlier stages.

Syrphid Flies (Hover Flies)

Adult syrphid flies (family Syrphidae) are commonly known as ‘hover‐flies’ and they are often associated with flowers, sap‐runs, and other sugary substances. Their name derives from the ability of the adult flies to hover in a fixed position. Syrphid larvae exhibit a wide range of feeding strategies, including predation, herbivory, and detritivory.

Among the syrphids, the larvae of Eristalis tenax (Drone fly) are the ones most likely to be encountered on a dead body. Their larvae are commonly known as ‘rat‐tailed maggots’ (Figure 8.8), because they have a long telescopic breathing tube. This acts like a snorkel and enables the larvae to breathe whilst the rest of their body is submerged. This ability means that they are most likely to be found during the middle stages of decay when the body has started to liquefy or if the body is partly submerged in stagnant water (Lindgren et al. 2015). When they finish feeding, the larvae crawl away in search of a drier environment in which to pupariate. The larvae of E. tenax colonise a wide range of fluid or semi‐fluid environments that contain high concentrations of organic matter, including sewage sludge and slurry. There are currently no accounts of E. tenax, or other syrphid species, being used as forensic indicators.

**Figure 8.8** Larva (top image) and pupa (bottom image) of the hoverfly *Eristalis tenax*. The telescopic breathing tube is a characteristic feature of this genus.

Piophild Flies

The family Piophilidae has a worldwide distribution but is relatively small and contains about 70 species. The majority of piophilid species develop on dead organic matter of some description. Adult piophilid flies are small and shiny‐black, which in a certain light gives a bright green or blue sheen. Piophila casei is the best known of the piophilids, as it is a common pest of stored products, but its larvae are also sometimes found on dead bodies. The adults are 3.5–4.5 mm long and although their larvae may grow to 10 mm in length, they are much thinner than the typical blowfly maggots. Its common name of the ‘cheese skipper’ results from the prodigious leaping capacity of the third instar larva. It achieves this by grasping its posterior region with its mouthparts so that the body adopts a ring shape, it then pulls hard to create tension and on releasing its grip, the insect is snapped into the air. Individual larvae travel up to 23 cm and achieve heights of 20 cm in a single leap. In addition to Pi. casei, several other species of piophilid have been recorded from human corpses, including Piophila megastigmata and Stearibia nigriceps (sometimes cited as Piophila foveolata or Stearibia foveolata). Russo et al. (2006) provide life history data for Pi. casei, and the use of piophilids as forensic indicators is reviewed by Martín‐Vega (2011).

Piophild larvae usually colonise corpses in the later stages of decay, when the body is starting to dry out, although there are records of them appearing earlier. Therefore, it cannot be assumed that the body must undergo several weeks/months of decomposition before piophilid colonisation begins. In addition to feeding on the dead tissues, the thin shape of the larvae enables them to penetrate the long bones and feed on the bone marrow. This will compromise the ability to extract DNA from the bones.

Stratiomyid Flies

Stratiomyid fly larvae are common soil invertebrates and they are often found on buried bodies or underneath bodies left on the soil surface. They have a characteristic flattened profile and a long conical head capsule, whilst their surface has a grained, leathery, appearance because of the deposition of calcium carbonate crystals in the cuticle (Figure 8.9). The adults are called ‘soldier flies’ because, in many species, they are brightly coloured and their scutellum (a shield‐shaped plate on the dorsal surface of the thorax) is armed with backwardly pointing spines. Stratiomyids are seldom mentioned in the forensic literature, although in America Hermetia illucens, the ‘black soldier‐fly’, has been used to estimate time since death in the absence of data from blowflies (Lord et al. 1994). It is often stated that H. illucens begin laying their eggs on a corpse once it is 20–30 days old and entering the advanced decay or putrid dry remains stage of decomposition. At this stage, blowfly maggot activity has declined or ceased entirely and in their place H. illucens larvae may become the dominant insect fauna on the corpse. However, in some circumstances, it may colonise a corpse that is less than seven days old and therefore still relatively fresh (Tomberlin et al. 2005): this clearly has implications for any estimations of the PMI that are based on its stage of development. H. illucens has a widespread distribution that includes the USA, parts of Asia, and continental Europe. It is currently not found in the UK, although it is probably only a matter of time before it establishes itself.

**Figure 8.9** Final instar stratiomyid larva. Stratiomyid larvae are common soil invertebrates, but they occur in large numbers within the skull and bones of dead animals when these reach the putrid dry remains stage of decomposition.

Trichocerid Flies

Trichocerid flies are commonly called ‘winter gnats’ or ‘winter crane flies’, because mating swarms of the adults dance above lawns, fields, and hedgerows during the winter, even when snow is on the ground. The adult flies are also seen during the spring and autumn, but less common during the summer months. The family Trichoceridae contains about 170 species, but there are only 10 species in the UK. The adults are thin delicate flies with long legs and long antennae that resemble small crane flies (daddy‐long‐legs). The larvae are long, thin, and cylindrical, with a well‐developed head capsule (Figures 8.10a and b) and a number of them are detritivores. Trichocera saltator has been found on human corpses and they are most likely to be found during the winter period when blowfly activity is reduced.

**Figure 8.10** (a) Trichocerid larva. Note the well‐developed head capsule. (b) Scanning electron micrograph of the anterior of a trichocerid larva.

8.2.1.1.2 Coleoptera

The order Coleoptera, better known as the beetles, comprise 25% of all animal species described to date. They are found in diverse habitats and exhibit a range of life styles – including the colonisation of dead bodies (Table 8.3). They vary in size from minute species less than 1 mm in length to some of the largest insects in the world, which can measure almost 17 cm and weigh over 100 g, but their basic morphology is very similar. They exhibit complete metamorphosis in which there are egg, larva, pupa, and adult stages of development. The adults have biting mouthparts and usually have two pairs of wings. The membranous rear pair of wings provide propulsion, whilst the front pair, known as the elytra, is hard or leathery, and provide protection. The rear pair of wings folds away beneath the elytra when not in use, whilst the elytra fold down above them so that they meet at the mid‐line of the dorsal surface. Beetles are therefore quickly distinguished from heteropteran bugs in which the front wings overlap when they are folded down; heteropteran bugs also have piercing mouthparts.

Table 8.3 Coleoptera families of forensic importance.

Suborder	Example Family of forensic importance	Notes
Archostemata	None	Wood eating, do not occur in Europe
Myxophaga	None	Alga eating, do not occur in Europe
Adephaga	Carabidae	Both larvae and adults are predators of blowfly larvae and other insects
Polyphaga	Staphylinidae	Rove beetles. Larvae and adults of some species prey on blowfly larvae and other insects.
	Silphidae	Burying beetles. Larvae and adults of some species prey on blowfly larvae and consume dead flesh.
	Histeridae	Larvae and adults of some histerid beetles prey on blowfly larvae and consume dead flesh.
	Dermestidae	Larvae and adults of some dermestid beetles feed on dry remains.
	Cleridae	Larvae and adults of some clerid beetles feed on dry remains.
	Nitidulidae	Larvae and adults of some nitidulid beetles feed on dry remains.
	Trogidae	Larvae and adults of some trogid beetles feed on dry remains.

Beetle larvae exhibit a range of morphologies, although most have six thoracic legs and a long soft abdomen. There are exceptions, such as weevil larvae, which lack legs. In some species, the legs are well developed and the larvae exhibit rapid movement, whilst in others, the legs are reduced and their power of movement is limited. The larvae have well‐developed head capsules and biting mouthparts.

Dermestid Beetles

The family Dermestidae contains over 1000 species. It includes many species that are common pests because they consume dry materials and stored products in domestic and commercial settings. Only a few dermestid species belonging to the genus Dermestes are regularly recovered from dead bodies (Figure 8.11a). Members of the genus Dermestes are often referred to as larder beetles or hide beetles, whilst their larvae are known as ‘woolly bears’ because of their numerous long setae. Their life cycles and habits are similar and their development times and the numbers of generations per year are strongly influenced by the environmental conditions. For example, Dermestes maculatus larvae develop to pupation within an average of 36.2 days at 65% relative humidity (r.h.), but take an average of 55.8 days at 35% r.h. (Katz et al. 1971). In addition to feeding on dry animal products, Dermestes ater also preys on the larvae and pupae of Musca domestica (Menezes et al. 2006) and whilst it is likely that other dermestids exhibit similar predatory activity, it is not known whether this would affect the colonisation of remains by other insect species. In laboratory cultures provided with moist food, the presence of even large numbers of dermestids does not stop the rapid co‐establishment of an unwanted phorid fly population.

Like most other insects, a peritrophic membrane separates dermestid midgut epithelial cells from the gut contents. This membrane facilitates the compartmentalization of the different phases of digestion and protects the underlying epithelial cells from pathogens. In dermestids, the faeces are voided still enclosed within the peritrophic membrane, so it emerges rather like a long, thin, pale Cumberland sausage (Figure 8.11b). The faeces, or ‘frass’ as insect faeces is called, is dry and crumbly, because dermestids have a highly efficient water retention system – this is partly why they are able to feed on dry remains. Some workers suggest that the presence of these faecal strands might be used to determine the PMI. However, they only establish that dermestids are present or were present in the past, even if the insects themselves cannot be located.

Both adult and larval dermestid beetles usually feed closely packed together. However, the adults are cannibalistic and should be kept separate from each other when collecting specimens. The risk of cannibalism means that the larvae burrow into any nearby material where they can be safe when pupating. Occasionally, they use bones and this results in 3–4 mm wide holes closely clustered together: these can be mistaken for puncture wounds.

In France, Charabidze et al. (2014) found that in 81 cases in which dermestid beetles were recovered from dead bodies, Dermestes frischii and Dermestes undulatus accounted for the majority of infestations (42 and 35.8% respectively). Dermestid beetles are usually associated with dry bodies and quickly reduce it to a skeleton. However, under experimental conditions, in which other insects are absent, adult D. maculatus will lay eggs on rats dead for less than an hour and in less than a month a starting population of 100 adult insects reduce a 500 g rat to a skeleton. When calculating the minimum time since death, it would therefore be unwise to assume that a body must have dried out before colonisation by dermestids begins. Interestingly, they also induce a localised increase in temperature similar to that observed associated with maggot feeding masses (Figure 8.11c).

Clerid Beetles

The adults and larvae of most species of clerid beetle are predatory, often feeding on other beetles. However, members of the genus Necrobia, in particular Necrobia rufipes and Necrobia violacea, feed on remains that are in the advanced stages of decay or drying out and these are commonly known as ‘bone beetles’. They are small – medium‐sized beetles (3.5–7.0 mm in length) and are often found in association with piophilid flies, presumably because they respond to the same chemical attractants. However, under experimental conditions, N. rufipes colonises freshly dead mice. The adult beetles congregate around the mouth and nose and within the ears. Therefore, like dermestids, one should not assume that a body must dry out before clerids colonise it. N. rufipes is an active beetle that flies readily, so it finds corpses quickly. The feeding activity of clerids, like that of dermestids, causes pits and scarring that must be distinguished from that caused at or before the time of death. Clerid beetles can establish populations in mortuaries without being noticed and then colonise a body within five minutes of exposure (Archer and Ranson 2005).

Nitidulid Beetles

Members of the family Nitidulidae are small beetles (2–6 mm) that are commonly known as ‘sap beetles’, because some species feed on sap oozing from plants. However, many species feed on decaying matter of plant or animal origin and some are pests of stored products. A few, such as Nitidula carnaria, colonise remains that are drying out and may comprise over 35% of the beetle fauna at this time. Although they feed on dry remains, some authors state that they prefer a warm moist environment and may be absent during hot dry months. According to Matuszewski et al. (2013), in Poland, nitidulids such as Nit. carnaria primarily colonise corpses found on open land and therefore their presence on a body found in a forest suggests that the body was re‐located.

Trogid Beetles

There are only four species of Trogidae in the UK and none of them are common, but their populations are more diverse and abundant elsewhere in the world. They are sometimes called ‘hide beetles’. This can lead to them being confused with dermestid beetles, unless the species name is provided. Their elytra are decorated with rough sculpturing that gives them a ‘warty appearance’, whilst their larvae have a characteristic ‘C’ shape. They are normally only found on dry bodies or those that are severely burnt. Presumably, they are attracted by dry, charred flesh. Another common name is ‘hair beetles’, because they are one of the few animals capable of digesting keratin. Keratin forms an important part of their diet and trogids are commonly found on the bodies of birds and mammals that have a thick pelage. They are less commonly found on human corpses – presumably, because we are relatively hairless.

8.2.1.1.3 Lepidoptera

The order Lepidoptera comprises the moths and butterflies and includes more than 180 000 species. Adult Lepidoptera are identifiable by the presence of scales that cover their body, two pairs of large membranous wings, and the possession of a long coiled proboscis. There are, of course, a few exceptions to this body pattern. For example, some of the clearwings lack scales on their wings, some female moths are wingless, and some of the primitive ‘micro‐moths’ retain functional mandibles. Larval Lepidoptera are commonly known as ‘caterpillars’. They have a well‐developed head capsule equipped with biting mouthparts, three pairs of true legs on the thoracic segments, and five pairs of fleshy prolegs on the abdominal segments. Most lepidopteran larvae feed on plants. However, a few species feed on dry organic matter, such as that found in bird nests and animal bedding, and these may also exploit dry corpses.

Pyralid Moths

Moths of the Family Pyralidae are sometimes referred to as grass moths or snout moths. They are small‐ to medium‐sized moths and have long narrow forewings and broad hindwings. The UK species typically have a wingspan of 15–35 mm and are usually undistinguished shades of brown and grey. Although the larvae of most species feed on plants, the Family includes several important pest species (e.g. the waxmoth Galleria melonella and the flour moth Ephestia kuehniella) that feed on dried stored plant products. The larvae of the Aglossa caprealis and Aglossa pinguinalis will feed on dry corpses, but their normal diet is stored agricultural produce and decaying vegetation.

Tineid Moths

The Family Tineidae comprises over 2100 species. The adult moths tend to be small with a typical wingspan 10–15 mm, although both smaller and larger species are found. The scales on their head are held erect giving a ‘shaggy’ appearance, whilst the wings are long and slender and end in fringes. Unlike the pyralid moths, tineid moths hold their wings roofwise over the abdomen when at rest. Some species have a vestigial proboscis or it is absent entirely. These moths are unable to feed and rely entirely on reserves accumulated during the larval stage. In many species, the larvae protect themselves within cases they spin from silk and then camouflage with fragments of frass and the food they consume. The best‐known species are the common or webbing‐clothes moth Tineola bisselliella and the case‐bearing clothes moth Tinea pellionella. These are common household pests that normally feed on clothing and carpets, stored grain, cereals, and dry vegetable matter. However, they will feed on mummified or dry skeletonised remains. Tineid larvae can break down keratin in hair and fingernails. Consequently, they sometimes congregate in hair (Bucheli et al. 2010) and leave the skin shaven (Figure 8.12).

**Figure 8.12** Damage caused to a museum specimen of a dry stuffed rat by the larvae of clothes moths. Mummified human remains suffer similar damage. The hair has been lost and the damage to the ears could be misconstrued as pathology caused at the time or shortly after death.

A gravid female T. pellionella lays 40–70 eggs over approximately 24 days. The female moths do not fly actively whilst they are laying their eggs. A moth seen flying around a room is usually a male or a female that has finished laying its eggs. The eggs hatch in 7–37 days, depending on temperature and the larvae often spin a protective silken tube around their bodies. The larval period may last anything from two months to four years, depending on temperature, humidity, and the nature of their diet. Afterwards, mature larva pupates within its protective tube and the adult moth emerges after 11–54 days.

Like many other insects, the larvae of tineid moths avoid light and are thigmotactic, i.e. they orientate themselves to vertical surfaces. Consequently, two bodies within a room may be colonised at different rates. A body at the side of a room will tend to be colonised before one in the centre, and a body that is in full sunshine may be colonised later than one in a dark corner.

8.2.1.1.4 Blattodea (Cockroaches and Termites)

The cockroaches and the termites were once considered separate orders, but molecular studies indicate that they are closely related. They are both now placed within the Order Blattodea. Within this order, there are several distinct families of cockroaches, although most of those of forensic importance belong to the Blattidae.

Blattidae (Cockroaches)

Cockroaches are small‐ to large‐sized (10–90 mm in length) insects, with a flattened body profile that enables them to hide in crevices, well‐developed running legs, long antennae, biting mouthparts, and two pairs of large wings. They are generally nocturnal and emerge at night to forage for food. Cockroaches are primarily tropical insects and exhibit hemimetabolus development, in which the egg hatches to release a first instar nymph that resembles the adult insect. With each successive moult, a nymph becomes more similar to the adult stage. After the final moult, the insect is an adult and has functional wings and genitalia; there is no pupal stage. Some cockroach species form huge colonies and a few exhibit primitive social systems. Only those cockroach species that live in domestic and commercial settings have forensic significance.

Most cockroach species are omnivorous and consume virtually anything that is organic and does not move out of the way fast enough. Common pest species, such as Periplaneta americana and Blatella germanica, eat dry and moist stored products, waste food, faeces, and one another. In squalid housing, there can be large numbers of cockroaches and they will commence feeding on a dead body soon after death occurs. The marks may not be visible immediately but become obvious when the skin dries out. Lesions to the face, neck, and hands may be mistaken for pre‐mortem wounds, although there is no vital reaction (Denic et al. 1997). However, if a person is comatose through illness or injury before death, then cockroaches may begin feeding whilst a person is still alive. This makes wound interpretation more difficult – although the presence of cockroach faeces, if not the cockroaches themselves, provides an indication of what might have happened.

Termitoidea (Termites)

Termites are primarily tropical insects, although some species are found in southern Europe. They are all eusocial species and live in nests containing a reproductive female (queen) and male (king) and anything from tens to tens of thousands of non‐reproductive workers and other castes. Termites are commonly referred to as ‘white ants’, but they are not related to them and their social systems are arranged differently: for example, in termites there are both male and female workers, whilst in ants, bees, and wasps, the workers are all female. In addition, termites exhibit hemimetabolous development, whilst ants are holometabolous.

All termite species feed on plants, plant products (including paper), or fungi. They do not exhibit predation or an attraction to fresh animal remains. Nevertheless, some termites tunnel into bones and cause modifications similar to pathological lesions. This is most commonly associated with buried remains and termite species that build their nests below ground (e.g. Amitermes lunae). However, skeletonised remains on the soil surface will also be exploited. An indication of termite damage is the presence of small ‘star‐shaped’ indentations on the surface of the bones. In tropical countries, bodies become skeletonised very quickly and termites damage fresh bones as well as those that are many years old (Queiroz et al. 2017).

8.2.1.1.5 Acari (Mites)

The Acari (or Acarina) are currently grouped as a subclass of the Subphylum Chelicerata (that is, with the spiders, scorpions, and harvestmen). Unlike the insects, and other arachnids, it is impossible to distinguish different outer body regions in mites. This is because during evolution, the head and thorax fused to form a region called the prosoma and this then fused with the abdomen. In addition, they often have a hard, sklerotinised shield that covers all, or part of, their body. Most mites have a globular body shape and relatively short legs: the larval stages tend to have three pairs of legs, whilst the adults have four pairs of legs. However, there are several exceptions to this rule. In common with other Chelicerata, mites lack antennae but have specialised appendages called chelicerae and pedipalps. In the Acari, the chelicerae are often pincer‐ or stylet‐like in shape and used for feeding, whilst the pedipalps are leg‐like, pincer‐like, or non‐functional. Although members of the Acari have a wide variety of diets, they all ingest fluids.

Mites do not have wings and their small size limits how far they can travel under their own power. Nevertheless, mites are frequently abundant on corpses. The reason for this is that many species are phoretic – that is, they attach themselves to other organisms and ‘hitch a ride’ to the next feeding site. A good example of this is Myianoetus muscarum, in which the non‐feeding hypopus stage accumulate immediately above pupariae of flies such as M. stabulans and then attach to the newly emerging flies as they burrow to the surface (Figure 8.13). They usually attach to the dorsal surface of the thorax and abdomen, but sometimes a fly is totally coated in mites. Once the fly reaches a food source, the mites drop off and commence feeding and reproduction.

**Figure 8.13** Hypopus stage of the mite *Myianoetus muscarum*. The mites lack feeding mouthparts and attach using two large suckers at their posterior end.

The mite species composition changes as the body goes through its varying stages of decay. For example, gamasid mites (e.g. Macrocheles) tend to be abundant during the early stages of decay, and tyroglyphid and oribatid mites (e.g. Rostrozetes) are more numerous once the body has started to dry out. Some of the mite species feed on the corpse, others are predatory and feed on the detritivores etc., and some feed on the fungi and microbes that grow on the body. Because the development of mites is dependent upon the environmental conditions, it is theoretically possible to determine their time of arrival, and hence the PMI (Medina et al. 2013). Consequently, some authors consider mites to have great potential as forensic indicators (e.g. O'Connor 2009; Perotti et al. 2009). However, their use is limited by their small size and the scarcity of mite taxonomists.

8.2.1.1.6 Annelida (Earthworms)

The Phylum Annelida includes the marine ragworms, the terrestrial earthworms, and the leeches. ‘Worms’ are popularly associated with dead bodies. For example, one of the lines in the English folk song ‘On Ilkley Moor Baht’ at’ goes ‘then t’worms ‘ll cum and eat thee oop.’ (These lines translate from the Yorkshire dialect as ‘On Ilkley Moor without a hat’ and ‘then the worms will come and eat you up’.) However, the worms referred to in the song and in popular folklore are almost certainly the maggots of blowflies – anything small white and wriggly tends to be classed as ‘a worm’. Earthworms are a quite distinct group of organisms. To date, over 3000 species of terrestrial earthworm species are known, although only 26 of these (plus some introduced species with a restricted distribution) occur in the UK. Earthworms look superficially similar, but they have different ecologies. They are divided into epigeic, endogeic, and anecic species. The epigeic species (e.g. Eisenia fetida) do not burrow and live in leaf litter and manure where there is a high content of organic matter. Endogeic species (e.g. Octalasion cyaneum) eat their way through the soil and do not form permanent burrows. Anecic species (e.g. Lumbricus terrestris) form deep permanent burrows, but come to the surface at night in order to drag food down into their burrow. Some earthworms feed on decaying bodies, but they are sensitive to changes in pH and repelled by the seepage of acidic material into the soil.

8.2.1.1.7 Miscellaneous Invertebrates

Many soil invertebrates, such as nematodes, slugs, snails, Collembola, Diplura, Dermaptera (earwigs), and Diplopoda (millipedes) feed on human and animal remains – especially those that are buried or left on damp soil. However, they are seldom useful forensic indicators. This is because they are difficult to identify, they are not linked to a specific stage of decay, and they do not develop feeding entirely on the body. However, monitoring changes in the abundance and diversity of soil nematodes and Collembola is used in pollution ecology studies. In addition, the appearance of a large decaying body is, in some respects, a pollution incident. Therefore, it may be worth exploring how their populations change underneath or surrounding a dead body. In addition, some species are associated with particular ecosystems. Therefore, their presence might be useful if it is thought that the body was moved.

8.2.1.2 Coprophages

Coprophages are creatures that consume their own faeces or that of other animals. Although some invertebrates such as dung beetles are specialist coprophages for which faeces is their only food, many also feed on other sources of decaying matter. For many invertebrate species, therefore, coprophagy and detritivory are simply options that are indulged in to varying degrees. Coprophagic species are present when a body is coated with faeces (murderers sometimes desecrate their victim's body this way), when the gut contents are exposed through wounds (Figure 8.14) or the decay process, and when fouling of the clothing occurs before death.

**Figure 8.14** This sheep was eviscerated after death, probably by foxes or badgers. Exposure of the guts attracted dung feeding flies and beetles. The same process would happen with human bodies left exposed in the countryside.

8.2.1.2.1 Diptera

Muscid and Fanniid Flies

Several species belonging to these two families are commonly associated with faeces. Some species, such as Mu. domestica (Housefly), Fannia canicularis (Lesser housefly), and Fannia scalaris (Latrine fly), have adults that readily enter buildings and larvae that live in faeces or dead organic matter. Consequently, these species are common in unsanitary conditions and infest soiled clothing, even if the wearer is still alive. They may be found on corpses, especially if it is soiled with faeces or the gut contents are exposed.

Musca domestica requires relatively high temperatures to complete its life cycle and in the UK the adults usually do not appear outdoors until May–June. However, indoors they breed continuously wherever the temperature remains high enough. The female flies lay batches of about 150 eggs within crevices of the larval food medium. The eggs are difficult to see when laid on white material such as nappies or bandages. The larvae develop rapidly and the whole life cycle from egg laying to adult emergence takes only six to eight days under optimal conditions. Consequently, populations may build up extremely rapidly. The larvae do not cause myiasis, although they may be found in blood‐soaked clothing and hair. They are often found in clothing soiled by urine or faeces, and this infestation may begin before the wearer dies.

8.2.1.2.2 Coleoptera

Geotrupid and Scarabeid Beetles (Dung Beetles)

The families Geotrupidae and Scarabeidae include numerous species whose larvae develop on dung. In many cases, the adult beetles dig a nest in the soil into which they place a parcel of collected dung. They then lay their eggs on the dung and cover it with soil. On dead pigs, Jarmusz and Bajerlein (2015) found that adults of the geotrupid Anoplotrupes stercosus would arrive shortly after death, although numbers increase as the body enters the bloat stage of decomposition and they remain present throughout the decay period. The adults feed directly on the skin, particularly around the anus and may chew through the abdomen to reach the intestines and feed on these. They state that the beetles made numerous tunnels around and under the dead pigs, but it is not clear whether the insects were provisioning their larvae with flesh or faeces or both. In Brazil, the scarab beetle Coprophanaeus lancifer exhibits similar behaviour but on a more dramatic scale. It can arrive in such large numbers that it removes large amounts of flesh and its tunnelling activity is sufficiently extensive to cause movement of pig carcasses weighing around 60 kg (Ururahy‐Rodrigues et al. 2008).

8.2.1.3 Carnivores and Parasitoids

8.2.1.3.1 Coleoptera

Many beetles, especially certain carabid and staphylinid species, are important predators of other soil invertebrates during both their adult and larval stages.

Carabid Beetles

The family Carabidae contains over 40 000 described species and about 350 are present in the UK. They have well‐developed running legs and the rear wings are often vestigial or rendered unusable by the fusion of the elytra. They are almost all predatory species at both the adult and larval stage. Carabid beetles arrive as early as the active decay period and both the adults and their larvae feed on fly larvae and other insects, but their impact on the corpse fauna is not known. The larvae of many carabid and staphylinid beetles are similar in appearance (Figure 8.15), but can be distinguished from the shape of their legs. Carabid larvae have 6‐segmented legs, whilst those of staphylinid larvae are 5‐segmented. In addition, the legs of many carabid species end in two claws, whilst those of staphylinids have only one claw.

**Figure 8.15** Predatory beetle larvae. (a) Larva of a staphylinid beetle. (b) Larva of a carabid beetle. Although fearsome predators, the impact of these beetles on the establishment of maggots on corpses is probably small.

Staphylinid Beetles (Rove Beetles)

The family Staphylinidae is extremely large, with over 1122 described species in the UK. They are characterised by their shortened elytra that cover less than half the abdomen. The hind wings are often large and are stored carefully folded underneath the elytra. Staphylinids therefore have a superficial resemblance to earwigs, but they lack the terminal forceps. Most of the UK species are dark in colour, have a long, thin profile, and vary in size from minute species (0.7 mm) to the formidable ‘Devil's Coach Horse’ (Ocypus olens), that reaches 28 mm in length.

Most staphylinids are actively hunting predators at both the larval and adult stage. They are found on corpses at varying stages of decay, where they feed on the larvae of flies and other beetles. Whether they affect the establishment and population of other insects on corpses is uncertain.

Silphid Beetles (Carrion Beetles, Burying Beetles, Sexton Beetles)

In the UK, there are 21 species of beetle belonging to the family Silphidae and approximately 210 worldwide. Although many species are associated with corpses, the family includes examples of predators and herbivores. For example, members of the genus Silpha are predominantly snail hunters.

The genus Nicrophorus includes the eponymous ‘burying beetles’. They are sturdy beetles (9–30 mm in length) with clubbed antennae and shortened elytra, so that the last three or four abdominal segments are exposed (Figure 8.16). Several species have distinctive red or orange markings on their elytra. Their name derives from the adults burying dead animals, such as mice, upon which their larvae subsequently feed. The adults are strong fliers and can detect a dead body at a considerable distance. They are, therefore, often one of the first invertebrates to arrive at a fresh corpse.

**Figure 8.16** Silphid burying beetles: (a) *Nicrophorus vespilloides*; (b) *Thanatophilus rugosus*.

Several Nicrophorus vespilloides adults co‐operate in a burial and then fight to determine which one will lay her eggs on the corpse. They are incapable of burying an entire human corpse, but may inter bits if it has been dismembered. Alternatively, they may chew out hunks of tissue, which are then buried. After burying the corpse or body part, the female beetle lays her eggs above the carcass and then covers it with her hindgut secretions to inhibit the growth of bacteria and fungi. The eggs hatch after about 2.5–5 days. The female remains with the hatchlings and feeds them on her intestinal secretions until they reach the third instar, after which the larvae consume the dead tissue. The larvae can develop entirely upon the buried remains, but grow faster if fed by the parent. Larval development takes five to eight days. After the final instar, the larvae crawl off and pupate for about two weeks. The adult beetles then emerge, but do not reproduce until the following year.

The various Nicrophorus species exhibit different habitat preferences. For example, Nic. vespilloides is usually found in forests and woodland, whilst Nicrophorus vestigator prefers fields and open land. Even among the silphid beetles that visit corpses, not all show burial behaviour. For example, Necrodes littoralis usually feeds on the bodies of large vertebrates including humans, although the eggs are laid in the soil under and around the body. The emerging larvae then colonise the corpse, sometimes in thousands, feeding alongside the adults on fly larvae and the decaying body. In France, Ne. littoralis was recorded in 15% of 1028 forensic entomology cases. Although it primarily colonised corpses found outside, it was also found on those located inside buildings (Charabidze et al. 2016). The adults feed on blowfly larvae and on the tissues of the corpse and they will modify stab wounds. The removal of tissue by Nic. vespilloides and Nicrophorus humator can result in circular penetrating injuries that are similar to gunshot wounds (Figure 8.17) (Baumjohann et al. 2014).

**Figure 8.17** Post‐mortem wounds caused by *Nicrophilus vespilloides* and *Nicrophilus humator*.

*Source*: Reproduced from Baumjohann *et al*. (2014), © Springer Nature, with permission.

Currently, the utility of silphid beetles as forensic indicators is mostly a consequence of their potential to interfere with wound interpretation. It is uncertain whether their consumption of fly larvae would compromise the calculation of the PMI. In addition, burying beetle species act as transport hosts for Poecilochirus mites that feed on blowfly eggs. Silphid beetles that arrive early in the decay period, especially those that arrive within 24 hours (e.g. Thanatophilus micans), might be useful to determine the time since death. Because beetle larvae take longer to develop than Diptera larvae, they provide an extended time interval for the post‐mortem interval. However, more information is required on the factors affecting their development rates; Dekeirsschieter et al. (2011) provide an excellent review.

Histerid Beetles (Clown Beetles)

Histerid beetles are commonly found on decaying animal and vegetable matter. The majority of species are predatory as both larvae and adults. However, they also consume dead organic matter to varying extents. There are 52 species in the UK and about 3200 worldwide. They are small‐ to medium‐sized insects (UK species are 1–10 mm in length), usually oval shaped and with shortened elytra that leave the final two abdominal segments exposed. They have characteristic elbowed antennae that end in swollen clubs formed from three fused segments. Histerid beetles are strong fliers and tend to arrive on corpses several days after blowflies. During daylight hours, histerid beetles are usually found underneath the body. Therefore, they may be overlooked if sampling is only conducted during daylight hours. Some species consume the eggs and larvae of blowflies and other insects, although the consequences of this for the rate of decomposition are not known.

8.2.1.3.2 Hymenoptera

The Hymenoptera contains the ants, bees, and wasps and is a huge order that includes over 150 000 described species. They vary in size from some of the smallest insects of less than 0.15 mm in length to some of the largest, which can be 38 mm in length with a wingspan of 63 mm. They usually have two pairs of membranous wings, the front pair of which is the largest. The front and hind wings are coupled by a row of tiny hooks so that in flight they can act as a single unit. The order is divided into two sub‐orders: the Symphyta (which contains the sawflies and wood wasps) that lack the characteristic ‘wasp waist’ and the Apocrita (which contains the ants, bees, and wasps) that have a narrow waist formed by a constriction between the first and second abdominal segments and the fusion of the first abdominal segment with the thorax. Those species of forensic importance belong to the Apocrita.

Formicidae (Ants)

The ants belong to the family Formicidae – a large family that contains more than 12 000 described species (~50 in the UK), with representatives to be found in virtually all terrestrial habitats apart from Antarctica. Some estimates suggest that ants are the most abundant multicellular organisms on the planet. Ants are all eusocial insects and a colony typically consists of a single reproductive female (queen) and varying numbers of non‐reproductive female workers and other castes. Only the reproductive males and females have wings: the males die after mating and the females bite their wings off after their reproductive dispersal flight.

In tropical countries, ants can be the most abundant invertebrates found on a dead body and occur at all stages from fresh to dry remains. They may slow the establishment of the blowfly population through removing eggs and young larvae. However, they also feed on the corpse and thereby speed the process of decay. The extent to which they accelerate or retard decomposition depends upon the species, their abundance, and the local conditions. In Brazil, Sales et al. (2016) found a negative correlation between the abundance of the ant Pheidole radoszkowski on rat carcasses and that of flies, and that the ants could skeletonise a 280 g rat within 9 days. Not all ant species are carnivorous and therefore have an impact on decomposition, so correct identification is important. However, even species that are considered herbivorous, such as the leaf‐cutting ant Atta laevigata, will sometimes consume carrion.

Initially, ant feeding results in reddened or yellow‐brown blotches with scalloped edges where they have removed the surface layers of the skin. This results in parchmenting as the underlying tissue dries out. Continued ant feeding damages underlying capillaries and at dependent regions, this results in seepage of blood that has pooled through hypostasis (Heath and Byard 2014). The forensic importance of ants is therefore mainly a consequence of their potential for complicating the determination of the post‐mortem interval and wound interpretation. Nevertheless, Goff and Win (1997) estimated the PMI for a body discovered in a metal trunk from the time taken for an ant nest to develop within the trunk to the stage at which alate (winged) to produce reproductive castes.

Vespid Wasps

The larvae of all social wasps belonging to the family Vespidae are carnivorous and the adults prey on a variety of other invertebrates that they bring back to the nest to be consumed. A large wasp nest may therefore have an impact on the surrounding invertebrate fauna. Adult wasps also forage for scraps of meat from nearby corpses. Common wasp species such as Vespula germanica are attracted to both fresh and freeze dried meat baits and can be expected to feed on both fresh and dry remains.

Different wasp species appear to have preferences for particular groups of insects as prey. For example, in Brazil, Polybia scutellaris preferentially captures adult Diptera such as sarcophagids and muscids. Also in Brazil, Agelaia fulvofasciata was observed removing tissue from around the mouth, anus, and eyes of fresh dead pigs. However, as decay set in, the wasps moved their attention to preying on sarcophagid larvae (Barbosa et al. 2015). It is uncertain whether the consumption of sarcophagid larvae was a consequence of these being the main Diptera species present or a specific choice. The forensic importance of social wasps is therefore similar to that of ants.

8.3 Parasitoid Wasps

Parasitoid insects are those that lay their eggs within the bodies of other invertebrates, usually other insects. The eggs hatch within their host, but this is not usually killed until the parasitoid has completed its larval development. There are numerous families of parasitoid wasps among the Apocrita. Examples of parasitoid wasps attacking blowfly and housefly larvae or pupae include Nasonia vitripennis, Alysia manducator, Muscidifurax raptor, and Spalangia cameroni. This can result in the slowing of the larval or pupal development rate and, ultimately, the death of the parasitised insect.

Nasonia vitripennis is the best‐known species (Figure 8.18) and has a worldwide distribution. It has an unusually large host range and lays its eggs in the pupae of a range of blowfly, fleshfly, and muscid species. The adult female wasp uses her ovipositor to bore a hole through the puparium and injects venoms that induce changes in the host's physiology (e.g. suppressing the immune response and arresting development) before eventually killing it. After stinging the host, the wasp then lays her eggs on top of the developing pupa. This occurs 24–30 hours after the pupa forms, i.e. the point at which the third instar larval cuticle separates from the pupal cuticle and forms the puparium. After hatching, the wasp larvae feed on the fly pupa. The wasps pupate within their host's puparium and the adults chew their way out after 10–50 days, depending on temperature. A. manducator has a similar life cycle, but it lays its eggs directly inside the developing pupa.

**Figure 8.18** Scanning electron micrograph image of adult parasitoid wasp *Nasonia vitripennis*. This species lays its eggs within the puparium of blowflies, but other species lay eggs within the larvae and search for victims when blowfly colonisation commences.

Parasitoids can be locally abundant. Therefore, if blowfly larvae or pupariae are collected for rearing, a large sample size should be obtained to allow for parasitoid induced mortality. Because most parasitoid wasps only attack their hosts during a restricted stage of development, they could theoretically be used to calculate the PMI. However, the ability to do this is limited by the lack of data on how environmental factors affect their development. In addition, calculating the PMI is not simply a case of adding the time taken for the parasitoids to emerge onto the time taken for the fly larvae to reach their susceptible stage. This is because a range of interacting factors affects the development of parasitoids. These include environmental factors such as temperature and biological factors such as host size and physiological state, as well as the number of parasitoids developing within the host (Rivers and Dahlem 2014).

8.3.1 Invertebrates Leaving Dead Bodies: Ectoparasites

Ectoparasites live permanently or temporarily attached to the outer surface of their host. Fleas, body lice, and head lice leave their host soon after it dies and the body temperature declines. The sight of them crawling on top of a dead person's clothing therefore indicates that their host has not been dead for long. The so‐called human flea, Pulex irritans is no longer a common pest in the UK and people are more likely to encounter the cat flea, Ctenocephalides felis, and the dog flea, Ctenocephalides canis. We may harbour one or two fleas, usually acquired from our pets, but large numbers are only present in people suffering from neglect or living in unsanitary conditions. The same is true of the body louse Pediculus humanus humanus. However, the head louse P. humanus capitis (Figure 8.19a and b) is extremely common, especially in children, even among affluent families. Crab lice (Figure 8.19c) are relatively common among the sexually promiscuous and those who have a relationship with someone who is. Although known as pubic lice, they are also found on other coarse body hair, such as beards. There are unconfirmed reports that the numbers of pubic lice are declining because of the increasing popularity among both men and women of waxing to remove genital and body hair. Pubic lice are slow moving and unable to wander away from a dead body. The potential of ectoparasites to act as vectors of disease needs to be considered when handling them.

**Figure 8.19** Common human lice: (a) Human head louse *Pediculus humanus humanus*. (b) Egg (‘nit’) of *P. humanus humanus* attached to a scalp hair. The egg has hatched. (c) Human crab (pubic) louse, *Phthirus pubis* – these lice also occur on other coarse hair such as the beard and eyelashes.

8.3.2 Invertebrates Accidentally Associated with a Dead Body

Invertebrates that are not associated with the decay process may become accidentally associated with a body through becoming trapped in its clothing or from using the corpse as a refuge. Alternatively, they may become trapped inside the vehicle or container in which the body is found. If these invertebrates have a restricted geographical distribution, are associated with specific habitats, or are active at only specific times of year, this can provide evidence of a person's association with a particular locality at a particular time.

An interesting example of accidental association is provided by Magni et al. (2015). They describe how barnacles attached to the clothing and shoes of a dead man provided forensic information. The man's body was washed up in May on a beach in the Calabria region of Italy. The largest barnacles on the body were goose barnacles Lepas anatifera – a species that is normally found in open warm waters where the sea temperature is above 18–20 °C. However, Le. anatifera has a wide distribution and it has been described from cooler climates. Therefore, it is possible that the barnacles grew on the body whilst it was in the surrounding Tyrrhenian Sea rather than having drifted in from further away. Based on the size of barnacle shells and records of sea temperatures, the authors estimated that the body was floating for 65–90 days before it reached the shore.

Case Study: Blackfly Cocoons as Forensic Evidence

In the summer of 1989, a group of divers exploring a river in the US state of Michigan came across a submerged car. As in a scene from a horror movie, on looking through the car's windscreen they saw the body of a dead woman slumped in the driver's seat. The divers informed the police and the car was hauled out of the water. The registration number was still attached and therefore it was not long before the car's owner was traced. He stated that his wife had stormed off in the car on a foggy night a few weeks earlier in June after they had a row. When interviewed, he said that because she was upset, she was probably not driving carefully, lost her bearings in the mist, and drove into the river. Although sounding plausible, the police were suspicious because:

The woman had suffered contusions to the head that were not consistent with a car accident.
He had recently taken out a life insurance policy on his wife.
He had pawned her jewellery.
His neighbours stated that they had not seen the woman for months rather than the few weeks earlier in June.

None of this evidence was sufficient to charge the man with having murdered his wife. What was needed was an accurate indication of the time since death. Unfortunately, this could not be provided from the state of the body, because the water temperature was so low it remained in excellent condition. Instead, the essential information was provided by the numerous insect cocoons and cases attached to car's bumpers. The cocoons and cases were made by blackflies (Simulidae), midges (Chironomidae), and caddisflies (Trichoptera). Although the adult insects had emerged and flown away, it was possible to make an accurate identification from the structures they left behind. The blackfly cases were particularly informative, because they belonged to a species known to pupate (and make the cases) in late April and May. Consequently, the car must have been in the water at this time. No cases would have been found if the car entered the river in June or later. Blackflies are common species associated with fast flowing rivers. They spend their winter living as filter feeders attached to vegetation. By spring, they complete their development and move to a solid structure (such as a car bumper), where they weave a slipper‐like silken cocoon around themselves that is firmly glued to their support. Within the cocoon, the insect pupates and afterwards the adult floats to the surface and flies off.

This evidence helped to prove that the man was lying and the prosecution alleged that he had clubbed his wife to death before putting her body into the car and pushing it into the river. The man was found guilty of murder.

Original article: www.nwf.org/News‐and‐Magazines/National‐Wildlife/News‐and‐Views/Archives/1992/When‐Scientists‐Become‐Sleuths.aspx.

8.4 Insects on Buried Bodies

Unless they are colonised before burial, the fauna of buried bodies is reduced compared to that above ground (Gaudry 2010). The abundance and diversity of the soil fauna decreases naturally with soil depth, because of the difficulty of access, reduced oxygen levels, and lower nutritive rewards. The difficulty of access means that buried bodies tend to be colonised by invertebrate species that are already present, such as soil collembola, and those which are small enough to crawl through cracks in the soil to reach the body either as adults (e.g. phorid flies) or larvae (e.g. M. stabulans). The lack of data on Collembola is surprising considering their abundance in the soil, although Merritt et al. (2007) found thousands of Sinella tenebricosa on a body that had been resting in an unsealed coffin for 18 years.

There is uncertainty about the extent to which blowflies can exploit buried bodies. Most of the literature states that even shallow burial prevents blowfly colonisation. This is because the adult flies do not burrow (though they may follow cracks in the soil) and they usually require physical contact or close proximity with the dead body or fluids leaking from it before they lay their eggs. Consequently, they are unlikely to lay their eggs on the soil surface and leave the larvae to burrow down to locate their food after hatching. However, there are reports of extensive maggot populations on buried bodies. In some of these cases, the maggots were not identified, so they may have belonged to muscid and/or phorid flies. Alternatively, the blowfly maggots might have resulted from eggs deposited on the body before it was buried. Blowfly eggs and larvae develop normally if buried with the body. In addition, blowflies might colonise a body buried in a shallow grave if the overlying soil contains cracks or there are tunnels created by mice and rats through which the adult flies could crawl.

The muscid flies M. stabulans and Muscina prolapsa are able to colonise buried bodies by laying their eggs on the soil surface, after which the first instar larvae crawl down through the soil to reach their food (Gunn 2016; Gunn and Bird 2011). The larvae can locate remains buried at 40 cm in loose soil, but their burrowing ability is much reduced in compacted soil. Even if the remains are on the soil surface, the adult flies tend to lay their eggs on the soil around it rather than upon it. In addition, the larvae tend to stay in the soil underneath their food – although they move to the surface if the larval density is high. This habit of remaining in the soil may explain why they are not recovered more frequently.

Case Study: How a Thin Covering can Affect the Colonisation of Remains by Insects (Nuorteva 1977)

A young girl was murdered in Finland and her body hidden in a forest by covering it with moss and branches. When her body was eventually discovered, there were pupariae of Muscina levida (cited as Muscina assimilis) in the surrounding soil that were thought to have arisen from larvae that had developed on the body. Although there were also blowfly larvae present, these were at an earlier stage of development than would have been expected from the stage of decay (i.e. if they had arrived at the start of the decay period, the blowflies would have completed their larval development). It was suggested that the colonisation of the body by blowflies did not commence until vertebrate scavengers had removed some of the material that had been covering the body. By contrast, the Muscina colonised the body immediately and probably benefited from the lack of competition from the blowflies. The calculated time taken for the Muscina to reach pupariation was a close match to the time since the girl was killed.

The physical and chemical properties of the soil have a marked impact on the colonisation of a buried body by insects, although the consequences vary with the species concerned. For example, first instar larvae of the sarcophagids Eumacronychia persolla and Phylloteles pictipennis can locate baits buried in dry sand (Szpila et al. 2010), but burial in dry soil prevents colonisation of buried baits by M. stabulans and M. prolapsa (Gunn 2016). Presumably, sarcophagid larvae have adaptations to prevent excessive water loss. By contrast, Muscina larvae can colonise buried baits in extremely wet soil.

The widely distributed coffin fly, Conicera tibialis, is the best‐known insect associated with buried bodies. It gets its name from the ability of the adult flies to detect the presence of a corpse buried over a metre below ground and then to crawl down through cracks in the soil to reach it. Co. tibialis also colonises bodies left exposed above ground and they will find their way into coffins that are placed within crypts and mausoleums if the containers are not tightly sealed. Successive generations of Co. tibialis can occur within a coffin over a period of years. Martín‐Vega et al. (2011) report finding large numbers of live adult Co. tibialis and their empty pupariae from a coffin that had been buried for 18 years. Although it is possible that the flies bred below ground since the time of burial, there was a surprising amount of (saponified) tissue remaining. In addition, no larvae were found, which suggests that the flies all arose from eggs deposited at about the same time. Under natural conditions, female flies lay eggs over successive days. Therefore, after a few generations, one would expect the population to consist of all life cycle stages. This suggests that the dead body was colonised as a single event, probably shortly before the coffin was exposed. It also indicates that Co. tibialis can develop on extremely old remains.

The larvae of some staphylinid and carabid beetles are normal members of the soil invertebrate fauna and often found several centimetres below ground. It is therefore not surprising that they are occasionally recovered in association with buried bodies. There are reports of histerid beetles being recovered in both shallow and deep (90 cm) graves (Gaudry 2010). If adult dermestid beetles (D. maculatus) are buried with a suitable food source, they quickly make their way to the surface and they do not attempt to locate buried food.

8.5 Future Directions

We need more information on the basic biology of most invertebrates of forensic importance. For example, the flight habits of blowflies, fleshflies, and muscid flies in relation to different environmental conditions (e.g. wind and rain) and in different countries and regions within countries. There is still uncertainty on the extent to which remains are colonised by blowflies and other insect species during twilight or nighttime conditions. Similarly, it is uncertain how burial conditions affect colonisation of remains by both blowflies and other insects and how burial influences their subsequent development. It would also be helpful to know the extent to which there are differences in developmental rates between populations from different geographical regions under ‘normal’ aboveground conditions. Most experiments on competition to date have involved varying the number of an individual species of the same age. By contrast, most corpses contain mixtures of species and age ranges and this would be an area of research worth exploring.

Much of the experimental fieldwork done on the colonisation of remains by invertebrates involves bodies protected by metal cages. This is because scavengers such as birds, foxes, dogs, and badgers might dismember the body or drag it away, never to be seen again. However, this is exactly the scenario that happens in crime scenarios. There is a need for more realistic experimental designs to compare the sequence of colonisation in both protected and unprotected bodies.