CHAPTER 2
The British Species
IDENTIFICATION OF SPECIES
DRAGONFLIES ARE A rewarding group to study because, unlike most insect groups, there are relatively few species to get to know; they are large and easy to find and, after some practice, many species can be identified in flight and from photographs. One of the most obvious features of a dragonfly is its large eyes. The dragonfly’s world is a visual world. They recognise each other by sight, either by their striking colours or by their mode of flight and behaviour. And we too can hone our observational skills and soon learn to identify many species of dragonflies in the same way. Most species can be identified from their unique combination of markings, especially those on the abdomen. Many species are sexually dimorphic, that is the females and males of the same species have a different appearance (Figs 16 & 17, p.32). This means that twice as many types must be learnt, but also that it is often quite easy to tell the difference between males and females. For those species that are not sexually dimorphic, males can usually be recognised by the swelling under the base of the abdomen produced by the secondary genitalia, and females usually by the swelling or spike towards the tip of the abdomen formed by the ovipositor. Some species are very easy to recognise by their unique appearance. Aeshna grandis is the only British species of anisopteran to have amber-coloured wings. Others may require more detailed examination. For example, males of the Coenagrion species are identified by the shape of the small black marking on the top of the second abdominal segment. When viewed through binoculars, this marking is often visible, even on specimens several metres away. Some species can be identified reliably in the hand only by close examination of the anal appendages (e.g. Lestes, Corduliidae), or leg coloration and genitalia (e.g. Sympetrum) but, with experience, even species in these groups can often be identified without the need to net them. That said, it may be necessary to secure a voucher specimen (see Appendix 2). Sometimes visual, or even photographic, records are insufficient to permit secure identification, especially in species which differ in small subtleties of morphology.
Dragonfly larvae are much more difficult to identify than adults, especially in the early stadia. A few species have a characteristic appearance and can be identified in the field from the markings on the caudal appendages (Pyrrhosoma nymphula), the shape of the head (Anax imperator) or distinctive thoracic markings (Cordulia aenea). The number and shape of the abdominal spines can be a useful character for distinguishing species of Libellulidae, but these may be difficult to see if they are obscured by debris. Also, the extent of the development of these spines may depend on the presence of insectivorous fish. Other species can be distinguished only by close examination under a hand lens or low-powered microscope. For example, most species of Aeshnidae differ in the shape and relative lengths of the caudal appendages (epiprocts and paraprocts) but these are too small to see clearly with the naked eye. The shape of the labium and arrangement of labial setae also provide important characters in many groups, but the setation may only be visible in dead or anaesthetised larvae. There are no known characters that will reliably distinguish the larvae of Coenagrion puella and C. pulchellum or Sympetrum striolatum and S. sanguineum. The F-0 exuviae, the shed skins of larvae left on emergent plants after adults have emerged, of Anisoptera and Zygoptera are usually identifiable to species and provide the most reliable way of establishing which species are completing their life cycles at a particular site. However, the problems of identifying larvae should not be underestimated. The shape and appearance of the caudal lamellae of Zygoptera change greatly during development (Fig. 60, p.115), the number of labial setae can be highly variable and is not always diagnostic, and abdominal spines can be variably developed. There is still much work to be done to establish reliable characters for larval identification.
This book is not intended to be an identification guide. For this purpose, we refer you to other books which serve this function (Box 2). Instead, in this chapter, we review the broad distribution of dragonflies in Britain, and the factors thought to influence this, before describing the characteristics of each family that occurs in Britain.
SOME IDENTIFICATION GUIDES TO THE BRITISH SPECIES
Brooks, S.J. (Ed.) (1997) (4th revised edition, 2004). Field guide to the dragonflies and damselflies of Great Britain and Ireland. British Wildlife Publishing: Hook.
Cham, S. (2007). Field guide to the larvae and exuviae of British dragonflies. Volume 1: Dragonflies (Anisoptera). British Dragonfly Society.
Cham, S. (2008). Field guide to the larvae and exuviae of British dragonflies. Volume 2: Damselflies (Zygoptera). British Dragonfly Society.
Hill, P. & Twist, C. (1996). Butterflies and dragonflies: a site guide. Arlequin Press: Chelmsford.
McGeeney, A. (1986). A complete guide to British Dragonflies. Jonathan Cape: London.
Miller, P.L. (1995). Dragonflies. The Richmond Publishing Co. Ltd: Slough.
Nelson, B. & Thompson, R. (2004). The natural history of Ireland’s dragonflies. The National Museums and Galleries of Northern Ireland: Belfast.
Powell, D. (1999). Guide to the dragonflies of Great Britain. Arlequin Press: Chelmsford.
Hammond, C.O. (1977) (1983, 2nd edition revised by R. Merritt). The dragonflies of Great Britain and Ireland. Harley Books: Colchester.
Smallshire, D. & Swash, A. (2004). Britain’s dragonflies. WildGuides: Old Basing.
BOX 3
REGIONAL GUIDES TO BRITISH DRAGONFLIES
Averill, M. (1996). The dragonflies of Worcestershire. Mike Averill: Kidderminster.
Belden, T.A. (2004). Dragonflies of Sussex. Sussex Wildlife Trust: Chichester.
Benton, E. (1988). The dragonflies of Essex. Essex Field Club: London.
Brook, J. & Brook, G. (2001). Dragonflies of Kent. An account of their biology, history and distribution. Transactions of the Kent Field Club 16: 1-115.
Brownett, A. (1996). The dragonflies of Oxfordshire. Brookside Books: Banbury.
Cham, S. (2004). Dragonflies of Bedfordshire. Bedfordshire Natural History Society: Bedford.
Coker, S. & Fox, T. (1985). West Wales Dragonflies. Mountain Books: Mountain.
Collingwood, N. (1997). The dragonflies of Staffordshire. Stoke-on-Trent City Museum and Art Gallery: Stoke-on-Trent.
Dunn, R. & Budworth, D. (2005). Dragonflies in Derbyshire: status and distribution 1977-2000. Derbyshire & Nottinghamshire Entomological Society: Derby.
Follet, P. (1996). Dragonflies of Surrey. Surrey Wildlife Atlas Series 2. Surrey Wildlife Trust: Woking.
Gabb, R. & Kitching, D. (1992). The dragonflies and damselflies of Cheshire. National Museums & Galleries on Merseyside: Liverpool.
Garner, P. (2005). The dragonflies of Herefordshire. Herefordshire Biological Records Centre: Hereford.
Grover, S. & Ikin, H. (1994). Leicestershire dragonflies. Leicestershire Museums: Leicester.
Holland, S. (1991). Distribution of dragonflies in Gloucestershire. Mrs Twissell: Cheltenham.
Lockton, A.J. (Ed.) (1996). The dragonflies of Shropshire. Wildscan Ecological Consultants on behalf of BIOS: Shrewsbury.
Mendell, H. (1993). Suffolk dragonflies. Suffolk Naturalists’ Society: Ipswich.
Prendergast, E.D.V. (1991). The dragonflies of Dorset. Dorset Natural History and Archaeological Society: Dorchester.
Randolph, S. (1992). Dragonflies of the Bristol region. Bristol/Avon Regional Environmental Records Centre: Bristol.
Saunders, J.W. (1986). Dragonflies of Pembrokeshire. Pembrokeshire Coast National Park Authority: Pembrokeshire.
Saville, B. (Ed.) (1997). Dragonflies of the Lothians. Scottish Wildlife Trust: Edinburgh.
Smout, A.-M. & Kinnear, P. (1993). Dragonflies of Fife: a provisional atlas. Fife Nature: Glenrothes.
Taverner, J., Cham, S. & Hold, A. (2004). The dragonflies of Hampshire. Pisces Publications: Newbury.
Taylor, P. (2003). Dragonflies of Norfolk. Norfolk and Norwich Naturalists’ Society: Norwich.
Tyrell, M. (2006). The dragonflies of Northamptonshire. Northants Dragonfly Group: Northampton.
DISTRIBUTION OF DRAGONFLIES IN BRITAIN
The distribution maps shown in this book (Appendix 4) are based on records plotted at a resolution of 10 km2. The records have been built up over a period of about 160 years. The latest maps which appear in Appendix 4 have been updated to the year 2006 and are based on 363,959 records from 48,881 sites. They represent a massive effort from the amateur Odonata recording community. While these maps provide a good idea of the broad distribution of the British species, areas of Scotland1 and Ireland2 remain less well covered than England and Wales. The maps may also provide a rather optimistic view of the status of the British species. The records are largely based on sightings of adults and no account is taken of numbers seen, whether or not the species were breeding at the places in which they were seen, whether these were one-off sightings or if the species has been recorded over a period of many years at the same site. It is also unclear from the maps how many sites are present within each 10-km square. A species may be recorded consistently from a particular 10-km square over several decades but may actually be declining if it is being lost from a series of sites within that square. An actual range contraction will become visible on the map only when the species disappears from the last site in that square. For this reason, county maps, plotted at 1-km.2 or 2-km.2 resolution and based on breeding records, are much more useful as a conservation tool.3
Thirty-nine species of dragonflies are known to breed in Britain and Ireland today. These resident species are supplemented by another twelve or so migrant species which appear more or less regularly, often in small numbers, but sometimes in their thousands. Most of the migrant species are encountered in southwest England if they originate in western Europe, whereas migrants that have set off from central Europe are most likely to be seen in southeast England and East Anglia. Migrant species usually make landfall during late summer, but they can turn up at almost any time of year and in any part of Britain. Dragonflies seen at unusual times of the year and in unusual places should be looked at closely to confirm their identity because they could well be migrant species. Judging from past experience, a strong case exists for securing a voucher specimen of any such migrant encountered in Britain, and depositing it in a museum (Appendix 2). Records of migrants are compiled annually by the BDS (Chapter 10). Many of the species resident in Britain, especially Aeshnidae and Libellulidae, disperse after emerging from breeding sites and this can sometimes take solitary adults far outside their normal distributional range and habitat.
The local-scale distribution of dragonflies in Britain is governed by habitat preferences of individual species (Chapter 3). However, regional-scale distribution is controlled by climate. The British Odonata exhibit five principal patterns of distribution that are likely to be influenced by climate.
Widespread
Some species, for example Lestes sponsa, Pyrrhosoma nymphula, Enallagma cyathigerum, Libellula quadrimaculata and Sympetrum striolatum (Fig. 1), occur throughout Britain and Ireland and do not appear to be climatically constrained in Britain. Nevertheless, Sympetrum striolatum is less common in the northeast of Britain, suggesting that this region is too cold for it, because otherwise the species has broad habitat requirements.
Southern
Some species are restricted to the south of Britain, suggesting that the summers (or winters) are not warm enough for them to complete their life cycle elsewhere. Species having a southern distribution include Calopteryx splendens, Ceriagrion tenellum, Ischnura pumilio, Aeshna cyanea (Fig. 2), Anax imperator, Orthetrum cancellatum and Libellula depressa. These species are likely to respond to global
FIG 1. Sympetrum striolatum is widespread throughout Britain (Robert Thompson).
FIG 2. Aeshna cyanea is common in southern England, but becomes scarce in the north and Scotland (Robert Thompson).
warming by expanding their distributional range northwards. Indeed, some of them are already doing so (pp.295-6).
Northern
Species restricted to Scotland or having a predominantly northern distribution include Coenagrion hastulatum (Fig. 3), Aeshna caerulea, Somatochlora arctica and Leucorrhinia dubia. These species are likely to lose ground if current trends in global warming continue (see p.296).
FIG 3. Coenagrion hastulatum is one of the few British species with a northern distribution (Robert Thompson).
Continental
A continental climate is typified by hot summers, cold winters and low rainfall. As far as this can be expected in an island in the northwest of Europe, these conditions are found in southeast England. Species that appear to have a continental distribution in Britain include Erythromma najas (Fig. 4), Aeshna mixta, Libellula fulva and Sympetrum sanguineum.
Oceanic
Cordulegaster boltonii and Orthetrum coerulescens (Fig. 5) occur in the west of Britain, suggesting that they prefer the wetter summers and milder winters provided by the Gulf Stream. The absence of C. boltonii from Ireland may be an indication that the species did not arrive in England until after the land bridge between Ireland and Great Britain was inundated by the Irish Sea shortly after the end of the last ice age.
FIG 4. Erythromma najas is largely confined to central and eastern England (Robert Thompson).
FIG 5. Orthetrum coerulescens is most abundant in western Britain and southern England (Robert Thompson).
DRAGONFLY HABITATS IN BRITAIN
Within the broad-scale, predominately climate-driven distribution patterns of British dragonflies, the local distribution and abundance of species is strongly influenced by habitat availability. Whereas the restriction to southeast England of Libellula fulva probably reflects the influence of a continental climate, its patchy distribution within this region is tied to the availability of the slow-flowing rivers in which it breeds. Sympetrum danae has a predominantly northern distribution, but also occurs in parts of southwest and southern England. The virtual absence of this species from much of the English Midlands, East Anglia and southeast England probably reflects the paucity in this region of heathland and moorland, and bogs with acidic, nutrient-poor pools. Certain critical environmental variables such as nutrients and dissolved oxygen also influence the distribution of dragonflies. An oxygen-poor lake or sluggish, eutrophicated, lowland river may support a large population of the pollution-tolerant Ischnura elegans, while other Odonata species are absent. Similarly, physical factors have an impact on species distribution. Platycnemis pennipes is restricted to southern England by a requirement for a relatively warm climate. Locally it is found only on unpolluted, slow-flowing rivers and canals, although along the course of a river it may be absent from stretches that have undergone extensive bankside clearance of vegetation. In a study at Epping Forest, to the northeast of London,4 a population of Cordulia aenea was found to be centred on the largest pond within a large block of woodland, which functioned as a stem habitat (Box 6, p.76). Small populations were present at other ponds within that block of woodland which served as secondary habitats (Box 6). However, some other ponds within the forest had not been colonised by this species, even though they appeared to be suitable. These ponds were in separate woodland blocks divided from the population centre by housing and expanses of grassland. Evidently, adult Cordulia aenea did not disperse far from the emergence site and were reluctant to leave the woodland canopy.
In Britain, there are five key wetland types that support different assemblages of dragonflies. Relatively few species are confined to flowing water, and fast-flowing streams are species poor. Slow-flowing rivers may support a few specialist species, but many species that breed in ponds and lakes also breed in sluggish rivers. Most British species breed in standing waters, but sites that combine a mosaic of different wetland types have the greatest potential for high species diversity.
Ponds and lakes
Acid-water pools on bogs, heaths and moorland support their own specialist dragonfly fauna that will be considered separately. In addition, the ditches and dykes that support a rich diversity of aquatic plants and are typical of lowland levels and fens have several specialist dragonflies which are likewise discussed below. Ponds (Fig. 6) and lakes, farm and garden ponds, woodland ponds, gravel pits, reservoirs and shallow temporary pools support many generalist species that also breed in most of the other wetland types considered here, but also a few specialists that are not found elsewhere.
As interest grows in wildlife gardening, many people are now creating garden ponds (Box 23, p.281). If these ponds are kept fish-free, they will soon support many different dragonfly species, even in the heart of the largest conurbations. Species that may arrive in the first few years after creation of a pond, before the aquatic plants have occupied much of it, include Libellula depressa, Sympetrum striolatum, Aeshna mixta and Anax imperator. As the pond matures, these species may become less abundant, and others, such as Pyrrhosoma nymphula, Aeshna cyanea and Coenagrion puella, that prefer luxuriant plant growth and plenty of plant debris at the bottom, come to dominate the dragonfly fauna. Large lakes
FIG 6. This shallow pond on Hatchet Moor, in the New Forest, Hampshire, is ideal for dragonflies, having a profuse growth of aquatic vegetation and the sheltering, but not overshadowing, belt of trees (Robert Thompson).
will also attract these species but, in addition, other species that favour open expanses of water (e.g. Enallagma cyathigerum, Aeshna grandis), floating-leaved plants (e.g. Erythromma najas, E. viridulum) and patches of bare ground on the banks (e.g. Orthetrum cancellatum) may become established. Woodland ponds, large enough to let plenty of light into the water, and those with profuse growth of emergent vegetation, are likely to support Cordulia aenea, Somatochlora metallica (Fig. 7), Lestes sponsa and Sympetrum sanguineum. In Scotland, small, well-vegetated ponds may also support Coenagrion hastulatum. Coenagrion lunulatum occurs in small, mesotrophic, well-vegetated, clear-water lakes in Ireland.
Lowland rivers and canals
The slow-flowing lowland rivers of England are home to two of our least common species: Gomphus vulgatissimus and Libellula fulva. These rivers also support two other more widespread river specialists, Calopteryx splendens (Fig. 8) and Platycnemis pennipes. Other species which commonly breed in lakes and ponds frequently breed in sluggish rivers as well. Among these are Erythromma najas, Coenagrion puella, Enallagma cyathigerum, Ischnura elegans,
FIG 7. Some dragonflies, like this Somatochlora metallica, prefer shaded woodland ponds in which to breed (Robert Thompson).
Aeshna grandis and Anax imperator. All these species require rivers that have clear water with luxuriant growth of submerged, floating-leafed and emergent plants. In addition, a scattering of overhanging trees and plenty of tall herbs and grasses along the banks is usually beneficial (but see Chapter 3) (Fig. 9).
FIG 9. The River Rother at Stopham Bridge in Hampshire where both Libellula fulva and Platycnemis pennipes breed (Robert Thompson).
Streams and upland rivers
Fast-flowing streams and rivers support a less diverse dragonfly fauna than do their slow-flowing counterparts. Few of the species that breed in standing or slow-flowing rivers occur in fast-flowing waters. It is likely that the high current speed, lack of submerged vegetation and cold, unproductive waters make such habitats unsuitable for these species. Calopteryx virgo can be expected on the fast-flowing sections of streams and rivers that have overhanging trees and luxuriant growth of bankside vegetation. Cordulegaster boltonii (Fig. 10) is common on small, unshaded streams cutting through heathland and moorland, especially in the western uplands of Britain. Shallow, unshaded, trickling streams with a gravel bed (Fig. 11) support populations of the rare Coenagrion mercuriale.
FIG 10. A male Cordulegaster boltonii. This species is common on shallow moorland streams in southern and western Britain (Robert Thompson).
FIG 11. The warm, shallow, trickling waters of this calcareous flush at Latchmoor, in the New Forest, Hampshire, provide an ideal breeding site for Coenagrion mercuriale and Cordulegaster boltonii (Robert Thompson).
Bogs, moorland and heathland
Many of the widespread pond species shun acid waters, where they are replaced by a distinctive dragonfly fauna not found elsewhere. In waters that lack fish or are too acidic for them, anisopteran larvae are usually the top predators. As a result, large populations of dragonflies can be supported even in water that is relatively nutrient poor. At large bog pools the air may be filled with whirling male Aeshna juncea (Fig. 12), Libellula quadrimaculata, Orthetrum coerulescens and Sympetrum danae. In northern Britain these species may be joined by Aeshna caerulea and Somatochlora arctica, particularly where patches of woodland are present, and by Leucorrhinia dubia on more open bogs. On the heaths of southern England and Wales even the smallest bog pool may be attended by Ceriagrion tenellum, and shallow seepages are frequented by Ischnura pumilio. Both these species require warm, shallow water to complete development, but are not
FIG 12. Aeshna juncea is abundant on bogs, moorland and heathland (Robert Thompson).
FIG 13. Lough Beg in Killarney National Park, Co. Kerry, Ireland, supports a wide variety of acid bog specialists (Robert Thompson).
restricted to acidic habitats and also occur in suitable base-rich sites such as clay pits and fens. In Ireland, populations of Coenagrion lunulatum occur on cut-over bogs (Fig. 13).
Levels, fens and marshes
The flat, low-lying levels of Somerset, the river flood plains and coastal marshes of north Kent, south Essex, Pevensey and the Arun Valley in Sussex, and the fens and Broads of East Anglia (Fig. 14) typify grazing marshes and flood meadows that provide rich dragonfly habitat. Wet grasslands crisscrossed by ditches, some of which dry out during the summer, but which are rich in aquatic plants and dense stands of reeds and rushes, provide ideal conditions for some dragonflies. These are the haunts of many of our common and widespread pond and lake species but also of some less common species that specialise in these plant-choked waters, including Lestes dryas, Coenagrion pulchellum (Fig. 15), Brachytron pratense and Aeshna isosceles. The turloughs of western Ireland, those mysterious pools that fill from time to time, are favoured breeding sites for odonate species that are vulnerable to fish predation but whose life cycle allows them to tolerate
FIG 15. Coenagrion pulchellum can be abundant on marshes, levels and fens, but elsewhere is uncommon (Robert Thompson).
periods of drought. Foremost among them is Lestes dryas, which maintains large colonies at some of these sites.
SPECIES ACCOUNTS
There have been relatively few detailed studies of the larval duration (voltinism) of the British Odonata. In the following accounts, if no precise, published study exists on voltinism of a British population we have provided an inference (prefaced by ‘probably’) derived from a general impression stated in an authoritative source.
We have listed the families in systematic order, starting with the most primitive, least derived, families in each suborder. Genera and species are listed alphabetically within each family.
ZYGOPTERA – DAMSELFLIES
Calopterygidae – Demoiselles
The Calopterygidae includes two British species: Calopteryx splendens and C. virgo. Both are widespread throughout Europe. They are large, conspicuous, and characterised by their metallic green or blue bodies and, in males, by dark blue wing patches (Fig. 16). Females lack the dark blue wing pigmentation (Fig. 17). Both species are largely restricted to running waters. The extent of the wing pigmentation serves to distinguish the species. Males are strongly territorial, but territories are relatively small, so males may be present in large numbers at some sites, amongst emergent vegetation, often in dappled shade. Males vigorously defend their territories against rivals, and a single male may remain in the same territory for up to ten days. There the individual displays his own suitability and that of his territory to females in an elaborate courtship ritual involving wing fluttering and intermittently throwing himself onto the water surface. Copulation is brief, lasting less than five minutes. Males guard females during oviposition, although they do not remain in tandem. Females lay eggs endophytically into a wide variety of emergent vegetation. Eggs are ready to hatch after about 14 days. The larvae are large. They have long antennae and long legs and superficially resemble stick insects (Fig. 18). The caudal appendages are long, narrow, triangular in cross section and banded. The larvae live amongst plant debris at the bottom of the river and development of both British species usually takes two years.5
FIG 17. The wings of female Calopteryx virgo are suffused with the colour of amber. The white pseudopterostigma is present only in female calopterygids (Robert Thompson).
FIG 18. Larva of Calopteryx virgo in stadium F-0. Its long antennae are typical of Calopterygidae (Robert Thompson).
Calopteryx splendens (Banded Demoiselle) (Fig. 8, p.25) has a graceful, butterfly-like flight; the wing beat is slow. The males are especially conspicuous as they flit between sunlit patches under overhanging trees, the sunlight reflecting off the inky-blue patches on their wings and metallic blue bodies. The species is common in slow-flowing lowland rivers with a muddy bottom, and in lakes adjacent to rivers, in most of England and Ireland. It is absent from Scotland and the very north of England. Adults are on the wing between the middle of May and early September. Calopteryx splendens requires stands of emergent plants which are used as perches and oviposition sites. Its occurrence appears to be positively correlated with the height of riverside vegetation and to be negatively correlated with the height of bankside trees and the bank.6
Calopteryx virgo (Beautiful Demoiselle) (Figs 16, 17, 18) has a general appearance similar to C. splendens, but it is common on fast-flowing unpolluted rivers and streams with a stony bottom, so they rarely occur together.7 The species has a predominantly southern and western distribution in England, Wales and Ireland with outposts in the Lake District, North York Moors and western Scotland. Adults are on the wing from mid-May to early September. The species does not breed in polluted sites or those which have suffered from bankside clearance of trees and emergent plants. This species is semivoltine in the New Forest.8
Lestidae – Emerald Damselflies
There are only two resident species of Lestidae in Britain and Ireland, Lestes sponsa and L. dryas, but these have recently been supplemented by two vagrant species, L. barbarus and L. viridis, from continental Europe. Adult Lestidae are relatively large zygopterans. The bodies are metallic green, usually with pale blue pruinescence at the base and tip of the abdomen in males. The wings are unpigmented. Unlike other damselflies, which rest with their wings closed over the abdomen, Lestidae hold their wings half open when perched (Fig. 19). They breed in standing water that usually supports a dense growth of submerged and emergent aquatic plants amongst which the eggs are laid and the larvae live. Tandem pairs of L. sponsa adults often form away from the breeding site9 and copulation in L. sponsa and L. dryas may last 30-60 minutes.10 The pair stay in tandem throughout oviposition which may continue with the pair being fully submerged for up to 30 minutes.10 Eggs are often laid above water and can
FIG 19. The habit of perching with the wings held half open is characteristic of Lestidae, as seen in this male Lestes dryas (Robert Thompson).
FIG 20. Larva of Lestes sponsa in stadium F-0. Like other Lestidae, this species has conspicuously banded caudal lamellae (Robert Thompson).
withstand desiccation. Lestidae are the only British zygopterans that overwinter in the egg stage. The larvae are large and hunt prey actively. This makes them vulnerable to predation by fish. All lestid larvae, except Austrolestes colensonis in New Zealand,11 develop rapidly and complete development in a few months. This enables them to take advantage of temporary pools that dry out in late summer and so are fish-free. The larvae have large caudal appendages that are lamellate and characteristically banded (Fig. 20).
Lestes viridis (Willow Emerald Damselfly) was recorded from a single male adult in Hertfordshire in 1899, but the authenticity of this record has recently been disputed.12 The first and only fully authenticated record in this country was of a F-0 exuvia collected on the North Kent Marshes in 1992.13 The species is widespread in most of Europe, although absent from Scandinavia.14 It breeds in a wide variety of standing and slow-flowing waters that are lined with trees and shrubs, especially willow, into which the female inserts her eggs.15 The eggs overwinter and larvae develop within three months after hatching in spring.15 Adults are on the wing from June to November, peak numbers appearing in August and September.
Lestes barbarus (Southern Emerald Damselfly) was first recorded in Britain in Norfolk in July 2002.16 Subsequently it was recorded in 2003 at the same site and at an additional location in Kent.17 So far only five specimens have been seen, and none was recorded in 2005,18 so it is too soon to decide whether the species will become established in England. The Norfolk site was a shallow, muddy coastal dune pool with no submerged vegetation but some emergent plants. This is typical of sites used by the species in continental Europe. The species also breeds in brackish water.19
Lestes dryas (Scarce Emerald Damselfly) (Fig. 19) is rare in England where it occurs around the Thames estuary, north Norfolk and at a few sites in the Midlands. It is commoner in Ireland. It favours shallow freshwater or brackish-water pools and ditches,20 which may dry out in late summer and support dense emergent vegetation, or ponds with naturally fluctuating water levels, such as turloughs in Ireland2 and some pingos in Norfolk.21 Such sites are liable to become totally overgrown and eventually permanently dry, so a succession of densely vegetated pools in an area is necessary for the continued local survival of the species. Over-abstraction, nutrient enrichment and overgrazing all threaten the suitability of sites for the species. Lestes dryas is on the wing from the end of June until the end of August.
Lestes sponsa (Emerald Damselfly) (Fig. 20) occurs throughout most of Britain and can be common locally. Adults are usually seen lurking amongst dense emergent vegetation near a wide range of standing waters, including ponds, lakes, canals, bog pools and brackish coastal pools. Excessive clearance of aquatic plants from a breeding site can reduce numbers. Adults are on the wing from late June until the end of September.
Platycnemididae – White-legged Damselflies
Platycnemis pennipes (White-legged Damselfly) is the only species of Platycnemididae currently resident in Britain, although two other species occur in western Europe. Males are characterised by their broad white tibiae. The abdomen is white in females and immature males, becoming pale blue in mature males. In Britain, the species typically breeds in slow-flowing rivers and canals supporting dense stands of emergent and floating vegetation. However, in France it commonly breeds in standing water, and in recent years there have been records of this habitat choice in Britain.22 Late-stadium larvae are easily recognisable by the appearance of the caudal lamellae which have dark patches and a long slender thread at the tip (Fig. 21). The larvae live amongst leaves and detritus at the bottom. Development probably takes two years.1 Males dangle their legs to display the broad, flattened tibiae when in flight, probably as gestures of threat, but there is no firm evidence that the legs are used in courtship display (Fig. 22). The legs are also used to stimulate the female during
FIG 21. Larva of Platycnemis pennipes in stadium F-0. Its caudal lamellae are mottled and each has a long, slender thread at the tip (Robert Thompson).
FIG 22. Male Platycnemis pennipes are characterised by their broad white tibiae (Ann Brooks).
copulation, which may last up to 30 minutes.23 Oviposition occurs in tandem, in groups with the male in the sentinel position. Eggs are laid into floating or emergent plants, but the female often descends below the water to continue laying into submerged stems.
Platycnemis pennipes is restricted to southern England where adults are on the wing from mid-May to mid-August. The species is locally distributed on slow-flowing rivers and canals, but can be abundant on well-vegetated, unpolluted waters where the adults perch amongst dense emergent plants, tall grasses and shrubs. The adults have a distinctive bouncing flight, but can be difficult to locate as they meander through the tall bankside vegetation. Platycnemis pennipes is vulnerable to pollution, but especially to the clearance of aquatic and bankside vegetation.23
Coenagrionidae – Blue and Red Damselflies
There are twelve species of Coenagrionidae currently resident in Britain and Ireland. Pyrrhosoma nymphula and Ceriagrion tenellum are red and black species, and the following are blue and black: Coenagrion hastulatum, C. lunulatum, C. mercuriale, C. puella, C. pulchellum, Enallagma cyathigerum, Erythromma najas, E. viridulum, Ischnura elegans and I. pumilio. The family is widely distributed throughout Europe. The British fauna includes a boreal element, comprising Coenagrion hastulatum and C. lunulatum, and a southern element, including Ceriagrion tenellum, Coenagrion mercuriale, Erythromma viridulum and Ischnura pumilio.
Coenagrionidae are small to medium-sized damselflies and are strongly sexually dimorphic. Females have more extensive black markings on the abdomen than males and can be difficult to distinguish at species level in the field. Males of the genus Coenagrion and Enallagma can be distinguished at species level by close examination of the shape of the black marking on the upper surface of the second abdominal segment. Adults of both sexes of the genus Ischnura exhibit several different colour forms, some of which are age related (Fig. 92, p.176). Different colour forms also occur in females of Ceriagrion tenellum, several Coenagrion species, Enallagma cyathigerum and Pyrrhosoma nymphula.
Adult coenagrionids can be abundant at freshwater sites, sometimes forming aggregations of hundreds of individuals. They typically have a weak fluttering flight, although Erythromma najas is more powerful. Males fly close to the water surface or perch amongst emergent vegetation at the water margin. Female coenagrionids may be encountered in fields remote from water. Mating is usually brief, lasting less than ten minutes, although Ischnura elegans may remain in copula for up to six hours (see p.250). Females oviposit endophytically, either accompanied by the male in the sentinel position (p.86) (Fig. 50, p.88) or, in the case of Ischnura, alone. Frequently the female descends completely below the surface of the water to lay eggs on submerged plant stems. Larval development of most species is completed within one or two years. Most larvae (Fig. 23) are claspers (p.118) and cling to the stems and leaves of submerged plants, but the larvae of some species, such as Pyrrhosoma nymphula, live amongst dead vegetation at the bottom. Most species have a long flying season and an unsynchronised emergence, having a Type 2 life cycle, although Pyrrhosoma nymphula is an exception (Table 6, p.170).
Ceriagrion tenellum (Small Red Damselfly) (Fig. 103, p.195) is restricted to warm, nutrient-poor, unshaded, shallow pools and seepages in acidic bogs or in calcareous mires, clay pits and slow-flowing shallow streams. Adults fly, while the sun is out, just a few centimetres above the ground and seem to disappear as soon as the sun is obscured by a cloud. Despite the red abdomen, they are surprisingly cryptic as they perch on low rushes and sedges. Ceriagrion tenellum has a patchy distribution in southern England and west Wales, and an isolated population exists in East Anglia. The species is local, and vulnerable to
FIG 23. Larva of Coenagrion puella, a typical coenagrionid, in stadium F-0 (Robert Thompson).
eutrophication, afforestation, shading, over-abstraction and dredging. The flying season extends from early June to early September. The larvae live in mats of sphagnum moss or debris at the bottom and take two years to complete development.24
Coenagrion armatum (Norfolk Damselfly) was last recorded in Britain in 1957.25 The loss of the species resulted from its breeding sites being encroached by reeds and willows and ultimately drying out.1 Populations are usually established in moderately eutrophic standing or slow-flowing water with dense submerged and aquatic vegetation. The life cycle has been little studied and the duration of the larval stage is unknown. Adults were on the wing in the Norfolk Broads from late May to mid-July.
Coenagrion hastulatum (Northern Damselfly) (Fig. 3, p.19) breeds in small, shallow pools, often overgrown with emergent vegetation, and so silting-up of sites is a threat. Larvae take two years to develop.26 The adult flying season is from mid-May until early August.
Coenagrion lunulatum (Irish Damselfly) (Figs 24 & 25) was first discovered in Ireland in 198127 and is now known to breed throughout central Ireland in
FIG 24. Like most other British Coenagrionidae, male Coenagrion lunulatum have a black abdomen with extensive patches of blue. This species is confined to Ireland (Robert Thompson).
FIG 25. In most female Coenagrionidae the upper surface of the abdomen is almost entirely black, as in this female Coenagrion lunulatum (Robert Thompson).
shallow mesotrophic lakes and bog pools with floating plants and sparse emergent vegetation. It seldom flies for long before perching on the floating leaves of aquatic plants.2 Large breeding populations are restricted to those sites not affected by drainage or nutrient enrichment. Probably due to these causes the species seems to have been lost from 25 per cent of its previously known sites in Northern Ireland since its discovery.28 The duration of the larval stage has not been studied in Ireland, but is likely to be one year or possibly two.2 The flying season extends from mid-May to late July.
Coenagrion mercuriale (Southern Damselfly) (Fig. 141, p.301) is rare in Britain and occurs only in shallow, slow-flowing, base-rich streams in parts of southern England and Wales. Adults of this small damselfly are seldom abundant even at stem habitats (Box 6, p.76)29 and fly a few centimetres above the ground, frequently perching. They do not stray far from the natal stream.30 High water temperatures in summer and winter are essential for the survival of this species and it avoids stretches that are shaded.31 Grazing favours this species by preventing the development of vegetation that may shade the breeding sites. The species is also vulnerable to eutrophication, over-abstraction and dredging. The species is semivoltine in the New Forest24 (Fig. 90, p.168). First-year larvae live in detritus at the bottom, but in the second year of development they move up into aquatic plants.32 Adults are on the wing from mid-May to early August.
Coenagrion puella (Azure Damselfly) is common and widespread throughout England, Ireland and southern Scotland. It prefers to breed in small ponds, including garden ponds, with dense vegetation. Adult males are often abundant, weaving through emergent plants or standing sentinel above ovipositing females, their vivid pale blue abdomens like shards of the sky. The species is sensitive to pollution although it tolerates eutrophication, but populations may be reduced by clearance of aquatic plants. Larvae live amongst aquatic vegetation and usually complete development within one or two years.33 Adults are probably not territorial.34 They are on the wing from mid-May until late August.
Coenagrion pulchellum (Variable Damselfly) (Fig. 15, p.30) has a scattered and local distribution in England, Wales and southwest Scotland, but is common and widespread in Ireland. It breeds in standing or slow-flowing water having luxuriant growth of aquatic and bankside vegetation and can be eliminated by dredging. It is similar in appearance and behaviour to C. puella but slightly more delicate. Larval development is completed in one or two years,35 and adults are on the wing from mid-May until early August.
Coenagrion scitulum (Dainty Damselfly) was known from two sites in Essex between 1946 and 1953 before catastrophic flooding by the sea rendered them unsuitable.1 Breeding sites in continental Europe are well-vegetated ponds, lakes and streams and the species also appears to be tolerant of brackish water in coastal marshes.36 Larvae live amongst aquatic vegetation and probably complete development in one year.36 Adults were on the wing in England from late May until late June.1
Enallagma cyathigerum (Common Blue Damselfly) (Fig. 98, p.185) is widespread and common throughout Britain. It breeds in a wide variety of standing and slow-flowing waters, but tends to prefer those with expanses of open water. Males are often abundant and characteristically skim across the surface of the open water or perch amongst emergent vegetation in groups of hundreds of individuals. The larvae live amongst submerged plants. Development is completed within one or two years,37 but in the north of its range development may take longer. Males are not territorial. The flying season lasts from May to early September.
Erythromma najas (Red-eyed Damselfly) (Fig. 4, p.20) occurs in southern England, where it can be locally common, but is absent from much of southwest England. It has recently extended its range north and west in Britain. The species favours large standing and slow-flowing waters with floating-leafed plants on which the males perch and fend off rivals. The species appears more robust than other coenagrionids. It flies close to the water surface but rarely comes to the shore, so its distinctive red eyes are best seen through binoculars. Females oviposit into the underside of the leaves of water lilies or use floating mats of dead reeds and rushes. The species may be lost from sites if these plants are removed by clearance, increased flow or boat traffic. The larvae live amongst aquatic plants and take one or two years to complete development.1 Adults emerge in mid-May and are on the wing until mid-August.
Erythromma viridulum (Small Red-eyed Damselfly) (Fig. 137, p.296) is the most recent addition to the resident British dragonfly fauna. The species was first recorded from Essex in 1999.38 After a large influx in 2001 it has now spread across much of East Anglia, the southeast of England and the Isle of Wight, and many inland counties including Cambridgeshire, Northamptonshire, Buckinghamshire and Warwickshire. Breeding has been confirmed at several sites. The species has been spreading northwards in Europe recently.39 This is a colonisation event caused by the expansion of the species’ European range rather than a series of migratory landfalls, and further consolidation and expansion inland in Britain is taking place (p.295). The species breeds in eutrophic ponds and lakes with floating-leafed plants. It closely resembles E. najas in behaviour and appearance. Mating pairs are attracted to patches of submerged plants, especially Ceratophyllum species (hornworts), close to the water surface.39 Duration of the larval stage is unknown. Adults are on the wing from July to early September.
Ischnura elegans (Blue-tailed Damselfly) is common and widespread throughout most of Britain, but more local in northeast Scotland. It is tolerant of moderate pollution and brackish water and is sometimes very abundant. The species breeds in a wide variety of standing and slow-flowing waters. At nutrient-rich sites it can be superabundant, rising in swarms as the emergent vegetation is parted, although it is less frequent at small garden ponds. The blue tip of the abdomen of this delicate damselfly is in striking contrast to the black of the rest of the abdomen. As an adult, the species is the most tolerant of all British species of bad weather. In exposed northern sites, it is often the only species present. Larvae live amongst aquatic plants and take one or two years to complete development,40 depending on temperature and food availability.41 The flying season extends from mid-May to mid-September.
Ischnura pumilio (Scarce Blue-tailed Damselfly) is rare in Britain, having scattered populations in south and southwest England, Wales and Ireland. The species is restricted to warm, shallow, unshaded pools and seepages with little vegetation. Suitable sites are maintained by disturbance, either by the grazing and trampling of cattle or by vehicles in mineral extraction sites. Shading of sites by encroachment of scrub can lead to local extinction.42 This small, delicate
FIG 27. The female Pyrrhosoma nymphula is marked with a greater extent of black than the male (Robert Thompson).
damselfly is rarely abundant or conspicuous, but the sight of the vivid orange aurantiaca phase female colour form (Fig. 95, p.178) is arresting. Larvae develop within one year43 and adults are on the wing from late May to July.
Pyrrhosoma nymphula (Large Red Damselfly) (Figs 26 & 27) is common and widespread throughout Britain and Ireland, breeding in a wide range of standing water habitats including garden ponds. Pyrrhosoma nymphula is the only odonate known to breed in Shetland.44 It is usually the first damselfly to appear in the spring, during late April, and is a welcome sign that the odonatological season has begun, but the flying season can be prolonged such that late-emerging adults can still be present in early September. Larvae live amongst plant debris at the bottom and complete development in two years45 or occasionally one year.46
ANISOPTERA – WARRIORFLIES
Aeshnidae – Hawkers
The family includes eight resident species: Aeshna caerulea, A. cyanea, A. grandis, A. isosceles, A. juncea, A. mixta, Anax imperator and Brachytron pratense. In addition, the following species are more or less frequent migrants: Anax junius, A. parthenope and A. ephippiger. Aeshnidae includes some of the largest species that occur in Britain. The larva of Anax imperator may reach over 55 millimetres in length and the adult has a wingspan of 105 millimetres. Adult Aeshna species have blue or green eyes with broad blue or yellow stripes on the sides and upper surfaces of the thorax, and characteristic rows of blue and yellow or green spots arranged in pairs along the upper surface of the abdomen. All species, with the exception of Aeshna isosceles, are sexually dimorphic, females having yellow or green abdominal spots and mature males having blue markings. Most species can be distinguished in the field, even when on the wing, by their distinctive markings. The thorax of Anax imperator and A. junius is green and lacks black markings; the abdomen has a black central upper stripe and the rest of the abdomen is blue in mature males but green in mature females (Fig. 29). Males of these two species can be distinguished only after close examination of the anal appendages and the marking on the vertex which, however, may vary greatly in outline.47 In both A. parthenope and A. ephippiger the abdomen is yellow-brown, with a black central upper stripe and a prominent blue saddle at the base.
Hawkers are so-called because of the habit of males of flying persistently when patrolling their prospective breeding sites. That is, they are fliers (p.233). In most species, individual males may be present at the same site for many hours, but males of Aeshna cyanea may remain for less than 40 minutes at a pool before moving elsewhere, and in this way time-share breeding sites between several males48 (Fig. 110, p.221). Similarly, males of A. caerulea do not remain long at any one pool.49 Male aeshnids tend to be aggressive, and frequent clashes occur between patrolling males. In the early evening they are often seen over rough grassland and hedges in large mixed-species foraging aggregations when aggressive behaviour is suppressed. Aeshnids do occasionally perch during the day (especially in overcast conditions) by hanging from the branches of trees and bushes (Fig. 30). Mating usually lasts more than ten minutes,50 and takes place amongst the foliage of bushes or trees or on the ground in long grass. It may last longer in poor weather. Females oviposit endophytically, usually unaccompanied by the male, except in the case of Anax junius, A. parthenope and A. ephippiger which often oviposit in tandem. Eggs are laid in submerged, floating or emergent plants or into rotting wood which may be protruding from the water, overhanging or even several metres away from the water (see p.82). Except in Anax imperator and Brachytron pratense, the eggs overwinter in diapause (Table 1, p.100; Box 16, p.167).
FIG 28. Larva of Aeshna mixta in stadium F-0. Aeshnid larvae typically have streamlined bodies, large compound eyes and short antennae (Robert Thompson).
Aeshnid larvae have smooth, streamlined bodies and large eyes (Fig. 28) and are typical claspers (Table 2, p.119), living amongst submerged vegetation and clinging to plant stems. They are active predators, often stalking their prey, which may include small fish and tadpoles. Species take from one to four years to complete development. Brachytron pratense and Anax imperator are Type 1 or spring species, passing their last winter as a F-0 larva in diapause and exhibiting synchronised emergence in spring or early summer, but the other aeshnids are Type 2 or summer species, emerging later and in a less synchronised fashion (Table 6, p.170).
Aeshna caerulea (Azure Hawker) occurs in northwest Scotland, and there is an isolated population in southwest Scotland. The breeding habitat comprises mossy bog pools, often in, or adjacent to, woodland.51 The larvae remain in this stage for three winters.52 Adults are seldom abundant, but may be seen basking in the sun on boulders or tree trunks, or flying low and fast around remote highland bog pools. They are on the wing from late May until early August.
Aeshna cyanea (Southern Hawker) (Fig. 2, p.18) is essentially a woodland species but is also frequently encountered over garden ponds where it readily breeds. Even in urban areas A. cyanea is a common visitor to gardens where its apparent curiosity will allow human observers to savour its rich green and blue pattern as it hovers close by. It occurs throughout England but becomes less frequent in the north, although it is currently expanding its range northwards. There are isolated populations in Scotland. It is a summer species and needs at least two years to complete larval development.53 Adults are on the wing from July until October and frequently fly after dusk on warm summer evenings.
Aeshna grandis (Brown Hawker) is common in lowland parts of central and eastern England and Ireland but is absent from most of southwest England and Ireland, and from most of Wales and Scotland. It breeds in a wide variety of standing and slow-flowing waters. On a late summer’s afternoon the sight of dozens gliding over a wild, uncut meadow, foraging for small insects, with the low sun making their wings shine like gold, can raise the spirits of an odonatologist jaded after a hot day in the field. The life cycle is thought to be completed in two to four years.1 The flying season extends from June to October.
Aeshna isosceles (Norfolk Hawker) (Fig. 140, p.299) is the least common of the resident British aeshnids, being restricted to the Broads and fens of northeast Norfolk and Suffolk. The vivid green eyes of adult males are not easily overlooked or forgotten. The species breeds almost exclusively in those ditches and dykes that support the floating aquatic plant Stratiotes aloides (Water Soldier),54 and is the only British species closely associated with a particular species of plant, although in continental Europe the association between Aeshna isosceles and this plant is not invariable (p.74). Stratiotes aloides will not survive in eutrophic sites and so Aeshna isosceles itself is vulnerable to this form of pollution. In addition, sea-level rise poses a prospective threat because most of the dragonfly’s breeding sites are at low altitude and close to the coast. The life cycle is probably completed in two years.1 The species is on the wing from early June until mid-July.
Aeshna juncea (Common Hawker) (Fig. 12, p.28) is widespread throughout western and northern Britain but rather local in, or absent from, much of southeast England. It typically occurs at upland pools and lakes on moors and bogs or in woodland. This is an aggressive species which frequently clashes with others of its own and other odonate species as it attempts to dominate the moorland pool it has selected as a breeding site. The larvae take two or more years to complete development.55 Adults are on the wing from late June until early November.
Aeshna mixta (Migrant Hawker) (Fig. 138, p.297) is common and widespread in southeast England and is spreading north and west. The species was recorded in Ireland for the first time in 2000,2 and populations have become established in north-east England in the last few years. In the 1930s the species was considered a scarce but regular migrant from southern Europe, having isolated breeding colonies in southeast England.56 The species breeds in a wide variety of standing and slow-moving fresh and brackish waters. It is frequently seen foraging in large aggregations along sheltered hedgerows or sunlit gardens and glades into the early evening. It avoids acidic pools and so is absent from heathland and bogs. Larval development is completed within a few months1 and so the species requires warm waters and is likely to extend its range in response to global warming. Adult males at breeding sites are less aggressive than other aeshnids. Aeshna mixta is the smallest of the British aeshnids and often forms foraging aggregations in the lee of hedges and trees in which adults dart to and fro and up and down at a height of several metres above ground. The flying season is from late July until early November.
Anax imperator (Emperor) (Figs 29 & 30) is common throughout much of southern England and Wales, although absent from uplands in this area, and has recently expanded its range northwards. It breeds in a wide variety of well-vegetated standing and slow-flowing waters, including garden ponds, which may support large numbers of larvae. The adult’s large size and its habit of flying high above the water rather than skirting the edges, sometimes hovering, sometimes gliding or incisively dashing forward, give it an almost regal air that is unmatched by other odonates. The flying season extends from early June until late August. The life cycle is usually completed in two years, but may be completed in one year if larvae have reached their penultimate stadium by the late summer of the first season (p.162).57
FIG 29. As in other female Aeshnidae, the abdomen of Anax imperator lacks the vivid, bright colours of the male, although sometimes old females can become blueish (Robert Thompson).
FIG 30. A male Anax imperator. Like other Aeshnidae he has large compound eyes and hangs vertically with wings outspread when at rest (Robert Thompson).
Anax junius (Green Darner) is common and widespread in North America, but in September 1998 six individuals were recorded in Cornwall and the Isles of Scilly.58 This is the first time that any endemic American species of odonate has been recorded in Europe (Appendix 2). The journey across the Atlantic was probably assisted by the passage of a hurricane passing up the east coast of North America.59 This species, unlike A. imperator, often oviposits in tandem.
Anax parthenope (Lesser Emperor) (Fig. 136, p.295), a migrant from southern Europe, is expanding its European range northwards and was first recorded in Britain in 1996.60 Since then, adults have been recorded in low numbers almost every year and successful breeding was recorded at two sites in Cornwall in 1999 when F-0 exuviae were found in small, well-vegetated ponds.61 In Britain it has been seen between June and September at localities as far apart as Cornwall and Orkney and several in between.
Brachytron pratense (Hairy Hawker) (Fig. 134, p.293) has a patchy distribution over southern England, where it appears to be spreading, and Wales. There are a few colonies in northeast England and western Scotland. It is widespread in central Ireland. The species frequents habitats that have a linear margin, including ditches, dykes, and canals that are rich in water plants. The larvae are frequent amongst dead vegetation, and females often lay into floating mats of dead reeds or rushes. This small, blue hawker is usually the first anisopteran of the year on the wing, but often offers only a fleeting glimpse as it zigzags between clumps of emerging plants at the edge of a fenland drainage dyke. The life cycle can be completed in one year,62 but a two-year larval development time is thought to be usual.1 Adults are on the wing from early May to late June.
Anax ephippiger (Vagrant Emperor) is a scarce migrant that turns up in Britain in low numbers rather infrequently. It was recorded only five times prior to 1980; between 1980 and 1998 there were eleven records, but it has not been recorded since. This last date coincides with a large increase in the number of sightings of Anax parthenope, which closely resembles A. ephippiger in flight, so it is possible that some of the earlier records of A. ephippiger were misidentifications. The 1971 record of A. ephippiger from the Shetland Isles and the Cornish record in 1988 are based on specimens deposited in The Natural History Museum, London. The species breeds in pools that are often temporary and saline, in sub-Saharan Africa and through the Middle East to Pakistan, but has never been recorded as breeding in Britain. Adults undergo long migratory flights and are apparently carried to Britain by strong southwesterly winds.63 Most individuals arrive in Britain in late summer and autumn.
Gomphidae – Club-tails
Gomphus vulgatissimus (Common Club-tail) is the only species of Gomphidae currently resident in Britain, although ten species are known from mainland Europe. A distinguishing feature of adults of the family is that, unlike other families of European Anisoptera, the compound eyes do not meet on the top of the head (Fig. 31). Adult G. vulgatissimus are of medium size and have yellow and black bodies, becoming green and black in mature males, and they have a distinctive swelling towards the tip of the abdomen. Adults are best seen when they are emerging in large numbers from slow-flowing rivers (especially the Thames, Arun and Severn) in early to mid-May. Gomphus vulgatissimus is a Type 1 or spring species (Table 6, p.170), and emergence is highly synchronised. After emergence the adults disperse into the hinterland, especially into adjacent woodland, and can be difficult to find.64 Males perch on shaded, tree-lined stretches of the river, patrolling close to the water surface. Females oviposit alone,
FIG 31. A young female Gomphus vulgatissimus. Her eyes do not meet over the top of the head, a feature characteristic of Gomphidae (Robert Thompson).
dipping the tip of the abdomen into the water to wash off the eggs. They usually breed in slow-flowing rivers, but will occasionally breed in standing water where a habitat is situated close to a river.65 The larvae burrow into the silt and debris on the river bed and are thought to take three to five years to complete development.66 The larvae are squat and differ from other anisopterans in having an enlarged third antennal segment (Fig. 32).
Gomphus vulgatissimus occurs on slow-flowing rivers in south-central England, the Welsh borders and southwest Wales where it can be locally common. A colony previously known in the New Forest until the 1960s is now probably extinct.1 Water pollution, dredging and clearance of bankside trees and woodland close to breeding sites may threaten populations. Removal of aquatic and emergent vegetation is not necessarily deleterious and the species is able to survive on rivers severely affected by boating that are no longer suitable for Platycnemis pennipes.66 Probably the surest way to see the adult is to time a visit to
FIG 32. Larva of Gomphus vulgatissimus in stadium F-0. This species is exceptional among Anisoptera in having a conspicuously enlarged third antennal segment in the larva (Robert Thompson).
one of the rivers on which it breeds so as to coincide with a mass emergence. On the right morning in May, hundreds of adults can be seen emerging on the bankside within a few hours. Adults are on the wing from early May until the end of June.
Cordulegastridae – Golden-ringed Dragonflies
Cordulegaster boltonii (Golden-ringed Dragonfly) is the only species of Cordulegastridae that occurs in Britain, although another five species are known from mainland Europe. This large, yellow-and-black-striped species frequents small moorland and heathland streams. A distinctive characteristic of adult Cordulegastridae is that the large green eyes meet at a point (as distinct from a line as in the Aeshnidae) above the head. Males (Fig. 10, p.26) and females are similar in colour, but the females have a distinctive, long, stout ovipositor protruding beyond the tip of the abdomen (Fig. 33), justifying the common name for the genus, ‘spike-tail’, used in North America (and Ireland, where it has never
FIG 33. The long ovipositor of this female Cordulegaster boltonii is characteristic of Cordulegastridae, as is the way that the compound eyes meet at a point across the top of the head (Robert Thompson).
FIG 34. The larva of Cordulegaster boltonii, here shown in stadium F-0, is a shallow burrower, usually living partly buried in stream sediments. The head is similar in shape to that of a libellulid but the abdomen is more elongate (Robert Thompson).
been recorded!). Adult males patrol long stretches of small streams, flying low and fast, close to the water surface, occasionally hovering or perching on overhanging vegetation. The males are not territorial in the strict sense, but will clash with other males of the same species which they encounter on their patrol flights.67 Females oviposit alone, using their robust ovipositor to thrust eggs deep into the substrate of the stream. The squat larvae typically live partly buried in detritus and gravel (Fig. 34) and probably take up to five years to complete development.1
Cordulegaster boltonii is common in southern, western and northern Britain where it breeds in shallow upland or heathland streams with a gravel substrate. It is worth searching for the spectacular larvae, which can be surprisingly abundant amongst gravel. The female is equally arresting when seen working like a pneumatic drill to insert her eggs deep into the substrate. Adults frequently perch amongst bushes of Ulex (Gorse) and are obligingly tolerant of the photographer. The species is not seriously threatened within its range, but populations may suffer from plantations of conifers which shade the water and limit larval habitats by reducing organic detritus and emergent plants.68 Adults are on the wing between the end of May and September.
Corduliidae – Emerald Warriorflies
This family includes three species currently resident in Britain: Cordulia aenea, Somatochlora arctica and S. metallica. A fourth, Oxygastra curtisii, formerly bred in Britain, but is now probably extinct here. The family has a predominantly northern and alpine distribution in Europe, which makes the species especially vulnerable to global warming. Adults are medium sized and metallic green with yellow or orange patches on the head and abdomen and bright green eyes (Fig. 35). Cordulia aenea, Somatochlora arctica and S. metallica, which may occur together at some sites, can only be distinguished reliably by close examination of the male anal appendages or female ovipositor. Oxygastra curtisii has distinctive orange-yellow spots down the upper mid-line of the abdomen. Male corduliids have a restless, inquisitive flight when at water, patrolling a stretch of the bank and performing frequent bouts of hovering. They usually remain for less than
FIG 35. The male Cordulia aenea, with its metallic green and bronze body and bright green compound eyes, is typical of Corduliidae (Robert Thompson).
FIG 36. Larva of Somatochlora metallica in stadium F-0. Its long legs and squat body, which are adaptations for hiding amongst leaf litter, are typical of Corduliidae (Robert Thompson).
30 minutes at the water. Mating takes place in the tree tops and is prolonged, sometimes lasting for over one hour.69 Females oviposit unaccompanied by the male, hovering over the water and rapidly tapping the surface with the tip of the abdomen. Females of Somatochlora metallica sometimes alight to deposit eggs into damp moss at the water’s edge.70 Away from water, adult corduliids are often seen feeding in woodland clearings where they may rest, hanging from branches or clinging to tree trunks. Corduliid larvae have squat, broad abdomens, long legs that extend beyond the tip of the abdomen and small eyes (Fig. 36). Corduliid larvae live amongst leaf litter and debris in the shallow margins and so populations are likely to be damaged by dredging and clearance of leaf litter or excessive removal of bankside trees. All are Type 1 or spring species (Table 6, p.170), exhibiting synchronised emergence of adults in spring or early summer.
Cordulia aenea (Downy Emerald) has a local distribution throughout southern and western England, with outposts in northeast Norfolk, western Scotland and the extreme southwest of Ireland. Larvae probably take three years to complete development71 and may climb several metres up bankside trees before emergence. Adults are usually encountered at ponds within large woodland blocks between mid-May and mid-July. The bright green eyes are often the first thing that draws the observer’s attention to a male as he darts, hovers and pirouettes in small bays along the banks of tree-lined ponds. In Britain, this species has probably declined following nutrient enrichment and the loss of woodland ponds. Its current, patchy distribution in Britain is probably the result of fragmentation of ancient forest.
Oxygastra curtisii (Orange-spotted Emerald) (Fig. 130, p.286) was known from small populations on the River Tamar, on the Cornwall-Devon border, and from the Moors River, in the New Forest, where the last individuals were seen in the early 1960s. The habitat was made unsuitable by sewage contamination and overshading by bankside trees.72 In Britain the species was known to breed only in slow-flowing rivers, but in continental Europe there are a few records from standing water..14
Somatochlora arctica (Northern Emerald) is rare, occurring only in northwest Scotland, and maintaining an isolated population in southwest Ireland. The species breeds in mossy bog pools in open woodland where population densities are low. Larval development is likely to take at least two years.73 Adults are on the wing from late May until late September.
Somatochlora metallica (Brilliant Emerald) (Fig. 7, p.24) has two centres of distribution, one in southeast England and the other in the Scottish Highlands. It is possible that the northern population may represent a postglacial relic whereas the population in southeast England may be the result of recent colonisation from continental Europe. Genetic analysis may shed light on the origins of these two populations. The southern population appears to be expanding at present.74 Somatochlora metallica is encountered from July to early September at large woodland ponds, lakes and lochs that have extensive margins of moss in Scotland and, in the south, also on slow-flowing rivers and canals sheltered by overhanging trees. The species is similar in appearance and habits to Cordulia aenea but seems less furtive, flying faster and further before pausing more briefly to hover, and being less reluctant to enter shaded overhangs. Larvae in southern England probably take two or three years to complete development.
Libellulidae – Chasers, Skimmers and Darters
There are ten species of Libellulidae regularly breeding in Britain and these are supplemented by an additional seven frequent or infrequent migrant species, some of which have bred in Britain. Adult libellulids are small to medium sized with a yellow, blue or red abdomen. Adults of most species are sexually dimorphic. The three species of Libellula have a dark patch at the base of each hind wing. The males of L. fulva and L. depressa (Fig. 38, p.61) develop a blue pruinescence as they mature, but the females remain yellowish. The abdomen is broad and stout in L. depressa, but more slender in L. fulva and L. quadrimaculata. Males and females of L. quadrimaculata are similar in colour, remaining brownish throughout life. The two British species in the genus Orthetrum have unpigmented wings, and mature males also develop blue pruinescence (Fig. 39, p.63) while the females remain predominantly yellow (Fig. 40, p.63). Orthetrum cancellatum is a large species. The male has prominent black markings on the abdomen, which has a conspicuous black tip. Orthetrum coerulescens is smaller and lacks black abdominal markings. Mature males in most species of the genus Sympetrum have a red abdomen (Fig. 43, p.66) (the abdomen is black in S. danae (Fig. 41, p.64), whereas the abdomen of females and immature males is yellow (Fig. 42, p.65). Species of Sympetrum (especially females) can be difficult to distinguish on the wing, and individuals often need to be examined at rest or in the hand when details of wing and leg coloration will usually permit identification (Appendix 2). Leucorrhinia dubia is characterised by its white face (Fig. 139, p.298). It also has a brown patch at the base of the hind wing. The abdomen is predominantly black, having yellow spots in the female and immature male. These spots become red in mature males.
Libellulidae breed in a wide range of standing and slow-flowing waters. The larvae are squat. Larvae of Libellula and Orthetrum are shallow burrowers (Table 2, p.117). They have short legs, live buried in the mud, silt and debris on the bottom, and their bodies are clothed with setae to which particles adhere. In contrast, Sympetrum and Leucorrhinia larvae (Fig. 37) are sprawlers (Table 2, p.119). They have longer legs and their bodies are not covered in setae. They live amongst submerged plants. Sympetrum larvae have a Type 3 life cycle (Box 16, p.167), completing development within one year, but development in the other genera is more protracted and may take up to three years. Emergence of adults is closely synchronised (in spring) in Libellula and Leucorrhinia but less synchronised in the other libellulids. Unlike aeshnids, libellulids are perchers (p.233). Adult males of most species are strongly territorial and are frequently observed perching, often in large numbers, on tall plants around the edges of ponds and lakes or on the banks of rivers. From there each male makes sallies to chase away rival males, catch prey, or pursue females, before returning to the same perch. Copulation in Libellula and Orthetrum species is often brief, lasting just a few seconds while in flight,75 or may be more prolonged and continue for a few
FIG 37. Larva of Leucorrhinia dubia in stadium F-0. This species is a sprawler, being squat, having relatively long legs and lacking a dense covering of setae (Robert Thompson).
minutes on the ground or a perch.76 In Sympetrum and Leucorrhinia species, copulation is usually longer, lasting from 5-60 minutes,77 and is completed while the pair are perched on the ground or amongst foliage. Species of Sympetrum usually oviposit in tandem, the male swinging the female down to the water to wash the accumulated eggs off the vulvar scale. After a few oviposition bouts the male releases the female and, like the other libellulid species, guards her while hovering nearby. Eventually the male may fly off, leaving the female to complete oviposition alone (p.86). Eggs laid in late summer by Sympetrum species may hatch within a few days, although most enter diapause and do not hatch until the following spring (see pp.98-9). However, in most libellulids the first winter is passed in the larval stage (Table 1, p.100).
Crocothemis erythraea (Scarlet Darter) is common and widespread in southern Europe and well known for its migratory habits. Since 1995 it has been recorded four times in Britain and is likely to reappear. It breeds in a wide variety of standing waters including those that are brackish or slightly polluted. The species is not easily distinguished (even in the hand) from C. servilia, a species liable to be imported with aquarium plants from the tropics (Appendix 2).78 Between 1980 and 2000 the breeding range of this species has been extending steadily northwards in western Europe.79
Leucorrhinia dubia (White-faced Darter) (Fig. 139, p.298) is a rare, resident species breeding in bogs in northwest England and northern Scotland. Its habit of resting on bare ground or low in vegetation makes it difficult to locate at first, but when disturbed it will suddenly fly off in an erratic manner for a short distance before settling again. The larvae (Fig. 37) live amongst submerged or floating mats of moss in bog pools. The species has recently been lost from Thursley Common, a nature reserve in Surrey, its southernmost site in England, apparently due to changes in habitat quality, possibly exacerbated by global warming. The species has a predominantly northern or alpine distribution in Europe and consequently can be expected to contract its range northward as average annual temperatures increase. Leucorrhinia dubia is also threatened by the destruction of bogs by commercial peat extraction by the horticultural industry, and by drainage and afforestation. It is likely that larvae require two years to complete development, although some individuals may complete it in one or three years.80 Adults are on the wing from mid-May to early August.
Libellula depressa (Broad-bodied Chaser) (Fig. 38) is common and widespread throughout southern England and Wales, but has recently increased its range
FIG 38. A male Libellula depressa. The blue pruinescence (a waxy secretion) develops as the insect matures (Robert Thompson).
northwards. It breeds in a wide variety of standing water sites, preferring non-acidic, open-water habitats in early successional stages with few aquatic plants. It is often one of the first visitors to a newly created garden pond where it will readily breed. The pond becomes less attractive to it as the aquatic vegetation develops, and L. depressa will become lost as a breeding species if the plants are not kept in check. The large size and broad, bright blue abdomen of the male makes him conspicuous as he patrols a garden pond. A rustling of wings may reveal a female repeatedly tapping the water surface at the edge of the pond, or she may be encountered as, resembling an enormous hornet, she suns herself on the outer branches of a bush (Fig. 107, p.201). Larvae can complete development in one year81 but two years are usually necessary.1 The flying season lasts from mid-May until early August.
Libellula fulva (Scarce Chaser) is restricted to short stretches of a few nutrient-rich, slow-flowing rivers in southeast England where aquatic and bankside growth of plants is well developed. The species is rare in Britain, although it may be expanding its range as water quality improves. A few new colonies have recently been discovered in Kent and on the River Wey in Surrey and Hampshire.82 This is one of the few species of Odonata in which the female outshines the male. The sight of the golden-orange abdomen and shining wings of an immature female perching on tall vegetation in the sun makes a rewarding climax to a visit to one of the lush lowland rivers where the species breeds. Libellula fulva is adversely affected by overshading, pollution, over-abstraction, dredging and canalisation. Larvae probably require two years to complete development.1 The flying season extends from late May to early August.
Libellula quadrimaculata (Four-spotted Chaser) (Fig. 111, p.229) is widespread throughout Britain and Ireland, breeding in a wide range of habitats including heathland, moorland, bogs, fens, canals, dykes, slow-flowing streams, gravel pits, lakes and ponds, and even brackish water. It is often abundant where it occurs, and the males are fiercely territorial. Swirling aerial ‘dogfights’ frequently develop as conspecific males clash over hotly disputed territories, or they engage other species, including larger aeshnids. The species is migratory, at least in mainland Europe, and is often encountered far from suitable breeding sites. Larvae probably take two years to complete development.1 Adults are on the wing from late May until mid-August.
Orthetrum cancellatum (Black-tailed Skimmer) (Figs 39 & 40) is common and widespread in southern England and Wales, and central Ireland, and appears to be extending its range northwards. It is a typical occupant of gravel pits, but breeds in a variety of pools, lakes and slow-flowing rivers. Males typically land on bare patches of ground or dry moss where they bask. Here they make a
FIG 39. The mature male of Orthetrum cancellatum frequently perches on dead tree trunks, bare ground or rocks (Robert Thompson).
FIG 40. A female Orthetrum cancellatum whose colour resembles that of an immature male (Robert Thompson).
tempting subject for the photographer, but more often than not, as the photographer settles to take the shot, the male will speed away to another basking patch just out of range. The species may be lost from sites in late successional stages. Adults often take relatively large insect prey such as butterflies, grasshoppers and adult Zygoptera. The larvae probably take two or three years to complete development.83 The flying season lasts from late May until early August.
Orthetrum coerulescens (Keeled Skimmer) (Fig. 5, p.21) is locally common at small pools and streams on bogs, where it has an affinity for even the most subtle flow of water, but is patchily distributed in southern and western Britain and Ireland. It is threatened by encroachment and fragmentation of heathlands, especially in Dorset, and by peat extraction. The males rise from perches around bog pools or clash over the open water, but are drab in comparison to the females with their gold-stained wings. Larval development probably takes two years.83 Adults are on the wing from early June to late August.
Pantala flavescens (Wandering Glider) is pan-tropical and a regular migrant. It has been recorded in Britain four times, most recently in 1989, but it is unlikely to colonise Britain. The species breeds in small, shallow, often temporary pools, where larvae develop very rapidly.84
FIG 41. A mature male Sympetrum danae. The habit of perching with wings swept forward on top of prominent vegetation is characteristic of many Libellulidae (Robert Thompson).
FIG 42. The immature male of Sympetrum danae has a coloration resembling that of the female (Robert Thompson).
Sympetrum danae (Black Darter) (Figs 41 & 42) is the smallest of the British libellulids. It is widespread and common in northern Britain and Ireland but is local further south where it is most frequently encountered on heathland, moorland and bogs. It has an erratic flight of short duration when put up from low moorland vegetation, but immature males can often be closely approached as they perch in rows on fences, basking in the low, late-summer sun. The species is not threatened nationally, but populations in East Anglia have been severely reduced in the last few decades by agricultural intensification and drainage. Like other Sympetrum species, adults disperse widely, and individuals may be seen far from breeding sites. Unlike most other libellulids, males are not strongly territorial. Larvae hatch in early spring and complete development within a few months. The flying season is from mid-July until mid-September.
Sympetrum flaveolum (Yellow-winged Darter) is widespread in Europe and an infrequent migrant to Britain. In some years (notably 1926, 1945, 1955, 1995 and 2006) huge numbers appeared in southeast and eastern England.85 Aggregations of adults are often encountered amongst tall grasses in meadows. The species breeds in shallow pools and in shallow, well-vegetated margins of lakes. The species has not established any long-term breeding colonies in Britain.
Sympetrum fonscolombii (Red-veined Darter) is primarily a tropical, migratory species whose distribution includes the Mediterranean region and which often migrates into northern Europe. It is a frequent migrant to Britain where it appears in most years, especially in southwest England. Recent major landfalls were recorded in 1992, 1996, 1998 and 2000.86 Recently, breeding has been sustained over a few years at some sites in Cornwall and Kent87 but there is no clear indication that the species has become established in Britain. It breeds in a wide variety of shallow, standing fresh or brackish waters.
Sympetrum meridionale (Southern Darter) has been recorded four times in Britain, most recently in 19011 (see Appendix 2). The species is common in the Mediterranean.
Sympetrum pedemontanum (Banded Darter) has been recorded once in Britain, during 1995.88 It occurs in southern central Europe where it breeds in marshes and is especially frequent in uplands. The species is expanding its range northwards in Europe and so may reappear in Britain in future.
Sympetrum sanguineum (Ruddy Darter) (Fig. 43) has a southeasterly distribution in England, Wales and Ireland, and is currently expanding its range in England
FIG 43. Like Sympetrum sanguineum, most mature males of Sympetrum species are predominantly red (Robert Thompson).
northward and westward. Suggestions that it may be a relatively recent colonist in Ireland appear to be unfounded, and new records are probably due to increased recorder effort.2 The species is usually encountered at ponds, lakes and marshes with extensive stands of emergent vegetation and often in woodland where the bright crimson of the male abdomen seems to glow in the semi-shade. Eggs are sometimes laid in vegetation, damp mud or hollows near the water’s edge,89 and do not hatch until they are covered with water in early spring. The species is a vagrant: migrants fly in from continental Europe each summer, and males are often encountered at water bodies where breeding does not occur. The shallow, well-vegetated sites in which the species breeds are likely to be damaged by clearance of emergent plants, dredging and succession of terrestrial plants. The life cycle lasts one year.11 The flying season extends from late June until early November.
Sympetrum striolatum (Common Darter) (Fig. 1, p.17) is one of Britain’s commonest species. It is abundant and widespread throughout most of Britain and Ireland but becomes less frequent in northeast Scotland. Populations in northwest Scotland and western Ireland are more extensively marked with black, leading some authorities to regard them as a distinct species which has been named S. nigrescens.90 However, the evidence for this is not compelling and S. nigrescens is probably only a melanic form of S. striolatum.91 The species breeds readily in most standing and slow-flowing waters, including brackish water. It is a frequent resident at even small garden ponds where it tolerates the close approach of the inquisitive odonatologist. Demonstrations of territoriality, oviposition, foraging, reproductive behaviour and larval habitat preferences are obligingly provided. Larval development is completed within one year.92 Adults can be seen from mid-June until as late as December in mild years when prey is still available. They are often seen basking on pale, insolated surfaces in autumn. The British population is sometimes supplemented by migrants from continental Europe.93
Sympetrum vulgatum (Vagrant Darter) is a rare migrant to Britain, but may be overlooked because of its close similarity to the abundant S. striolatum. The species is common and widespread in central and northeast Europe where it breeds in a wide variety of standing-water habitats.
OPPORTUNITIES FOR INVESTIGATION
Few hard data exist on the duration of the larval stages (voltinism) of Odonata in Britain. Some of the information given on voltinism is anecdotal or based on evidence derived from European studies which may not apply to the same species in Britain. The duration of the larval stage in a southern European population of a species is likely to be less than in a northern European population of the same species because rate of larval development is strongly influenced by temperature. Raising larvae in aquaria at home or in the laboratory is unreliable as evidence of voltinism in nature because it is difficult to duplicate outside temperatures and food availability, both of which have a significant influence on larval development rate.
It is not easy to obtain information on voltinism, but it is a subject on which the amateur odonatologist can make a useful contribution because it requires no expensive equipment but only patience, careful observation and field skills. Species emerging within one year of a pond being dug provide unequivocal evidence of a univoltine life cycle. The presence of different age cohorts in a larval population sampled in late autumn, winter or early spring can also provide useful inferences about voltinism. If larvae are absent in late autumn but very small larvae are present in spring, this suggests that eggs undergo a winter diapause and that larvae develop within a few months during the spring and summer. If only one age class of a particular species is present, this suggests a univoltine life cycle. If larvae in very early stadia are present together with final or penultimate-stage larvae this indicates a two-year or semivoltine life cycle. A three-year life cycle would be indicated if larvae in the earliest stadia were present together with mid-stage larvae and final-stadium larvae. This presupposes that the larvae can be accurately identified in all stages, which for several of the British species is not possible at present.