Humans are home to three louse species: head lice, body lice and crab lice (also called pubic lice). Each has its own favoured blood-sucking spot on the delicate human body.
Crab lice are easy to differentiate. They are small (1.1–1.9mm), broad, squat and rather crab-like, and they are easily the most embarrassing insects in the world. Let’s not go into too much detail about them, at least not until pages 108–9.
Head lice and body lice, on the other hand, are much more problematic. Adult body lice are slightly larger (2.3–4.1mm) than head lice (2.1–3.3mm), but there is plenty of overlap and in the laboratory, they interbreed resulting in intermediate lice.
Phthirapterists are still politely arguing over the differences (or similarities), but recent technological advances give a few clues. A study in 2005 looked at some unfortunates who were doubly infested with head and body lice. We don’t learn a great deal about them, but they were probably unfortunate down-and-outs, wretchedly poor and sharing the same grim rough-sleeping arrangements. Over several months, head and body lice were collected from each of them. DNA analysis of the lice confirmed that although each person had both types of louse, and although they moved from head to head and from body to body in the group, breeding as they went, they did not move between body and head, even on the same individual.
The head and body lice were genetically distinct, separate in habits and behaviour, isolated on different parts of the human body and they never interbred. They were different species.
This research is not just for mere academic interest. Body lice are associated with poverty, personal hygiene and dirt, and they spread disease. Thankfully, all we have to worry about are a few head lice
The body louse is the louse of war, famine and homelessness, the louse of the natural and the man-made disaster.
The body louse would be better called the clothing louse. One of its older scientific names, Pediculus vestimenti, echoes this. Most of the time, clothing lice hide in the dense weave of the clothes but move to the skin to feed four or five times a day. Just like head lice, they carefully glue their nits in place, but they attach them to the clothing fibres rather than to body hairs.
Much of what we know about lice today was discovered by studying the clothing louse. This was the louse of the desperately poor, the homeless, the refugee, the famine or earthquake victim. It was the louse of the foot soldier encamped for months in the cold wet trenches during the first world war. This was the louse of the natural or man-made disaster
Clothing lice can reach appalling proportions and finding 30,000 lice on a single person was all too common. Yet ironically, this is the louse that is easiest to get rid of.
All you have to do is take off your clothes. A change into clean clothes once a week will allow you to wash and air the lousy ones. Most lice and nits will be dead by the time you change back. Or if they are not, the few survivors will succumb next week.
Unfortunately, people suffering from clothing-louse infestations do not own a second set of clothes. They may, in fact, possess nothing but the clothes they stand up in, or lie down in. These are people who do not, who cannot, take off their clothes for weeks, or months or years.
Compared to the clothing louse, the head louse is a doddle.
Russian anti-louse poster, text reads: ‘Red Army squashed White Army’s parasites: Yudenich, Denikin, Kolchak. Now the Red Army has a new trouble – typhus louse! Comrades, fight with this infection! Do away with the louse!’
With the exception of malaria mosquitoes, the clothing or body louse has killed more people than any other animal on the planet. It has killed them by spreading three important diseases.
Typhus (Rickettsia prowazekii) is a bacterium causing fever, aches, cough, weakness and a blotchy rash. Some ‘plagues’ of the Middle Ages are likely to have been typhus, spread by lice, rather than the bubonic disease spread by fleas. A body louse drinking blood from a diseased person becomes infected as the microbes breed in its guts. The bacteria damage the insect’s intestines and the louse starts to pass copious bloody bacterial faeces. If the diseased louse moves on to another person, the faeces infect small cuts in the skin, which are usually the result of scratching. Depending on the strain of bacteria up to 60% of human victims die unless treated with antibiotics. Head lice, though, do not carry disease.
Trench fever (Bartonella quintana) is a similar organism, spread by body lice in a similar way. It is not usually fatal but is still unpleasant and debilitating. It came to prominence in the infantry soldiers huddled in the trenches of the first world war. Head lice, though, do not carry disease.
Relapsing fever (Borrelia recurrentis) is another type of bacterium. This time, the bacteria reproduce and lodge inside the louse’s body. They are released only if the body louse is crushed at the site of the itchy bites – a common enough event. Human mortality can reach 10% unless this disease is treated with antibiotics. Head lice, though, do not carry disease.
One more time. Head lice do not carry disease.
Not to be confused with typhoid, another bacterium Salmonella typhii, spread in contaminated food or water.
*You can substitute the name of any town you like here – crabs aren’t fussy.
Crablice are so named for obvious reasons. They are broad, fat, stout lice and with extra-large heavy claws on their middle and back legs, there is definitely something crab-like about them. They are also called the pubic louse for other obvious reasons: they inhabit the nether regions. Here, they cause intense itching and the bites can become inflamed, causing small raised purple spots. Needless to say, crabs are also the most embarrassing lice, and rarely talked of in polite society.
It’s not really that crab lice have a predilection for the groin and their spread by casual sex is sometimes overemphasised. It is more to do with the fact that they have broader bodies and stouter claws, adapted for clinging to the coarse, more widely-spaced pubic hairs rather than the finer and closer scalp hairs.
Just like head and body lice, they get around by physical contact, in this case usually in shared double beds. The French called them papillons d’amour 
‘butterflies of love’. However, crab lice do have a tendency to wander around the body, especially the hairy human male, and they will visit chest and armpit, beard and moustache. It’s easy to see, then, that they can get transferred onto innocent victims and there are regular reports of children having crab louse infestations in the eyelashes.
A very small number (less than 1%) of louse infestations on heads turn out to be crab lice. These unusual outbreaks are usually on red-headed people, whose thicker hair strands are spaced slightly further apart. This is an exceedingly embarrassing louse.
They can still be combed out though.
Studying head lice can tell us some remarkable things about our own history such as when humans first started wearing clothes. There was always an assumption that body lice evolved from head lice in response to the ‘new’ human fashion of wearing clothes, rather than walking around naked. Now we have firm evidence not just that this occurred, but when it occurred.
DNA, the stuff of our genes, can now be examined at the molecular level. This is the DNA sequencing often used in evidence in court cases, or at least in TV dramas. The molecules of DNA sometimes get damaged or altered, just a tiny bit, and these chance mutations gradually build up to give the variation we see in all living things.
We know the rate at which these changes occur naturally. So by looking at DNA molecules from different animals, we can work out how long the differences have taken to occur, and from that we can estimate how far backwards in time an evolutionary split happened.
In 2003, researchers looking at the DNA of head lice and body lice from all over the world made a clear discovery. Body lice evolved from head lice about 72,000 years ago.
This fits in very neatly with the fact that humans started moving out of Africa at about this time into cooler regions where clothes would have been a definite advantage. There is no direct archaeological evidence of clothes from this time. They have all rotted away to nothing. But the first clothes-based tools – needles – start to appear about 40,000 years ago. It took just a little bit longer for nit combs to appear.
We know quite a lot about louse lives the different sex ratios, preferences for temperature and humidity, daily and nightly movements, feeding rates, sexual foreplay, egg-hatching and survival rates. We know this not from randomly checking lousy heads or keeping infested schoolchildren in the observation lab, but from maintaining experimental colonies.
Louse researchers have tirelessly dedicated their own bodies to the advancement of science and have kept the insects they study as personal pets. It is possible to keep lice in a glass tube with a twist of damp paper, but they have to be kept warm and they have to be let out onto the skin to feed at least twice a day. It’s all a bit fiddly and not ideal. It’s better to wear the lice
Delicately crafted cardboard boxes in which to house lice were first made by bacteriologist George Nuttall and described to an eager louse research world in 1917. The bottom of the box was cut out and lined with fine silk with a tight, regular mesh. It was developed for milling flour but proved perfect for keeping the lice in whilst allowing them to feed through it.
Several boxes of lice could be worn in the sock-top, although, as was pointed out, this is hardly compatible with a short skirt and silk stockings. Female researchers were not let off, though, and a stylish louse garter was created to be worn above the knee.
Polish phthirapterist Rudolf Weigl employed 50 people to feed his stock of 350,000 lice. This was big business.
Today, it is possible to keep laboratory head lice in enclosed containers and let them feed on stored human blood through an artificial membrane. It’s all a bit impersonal and antiseptic though.
1 Dog louse Trichodectes latus |
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2 Human crab louse Phthirius inguinalis |
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3 Peacock louse Goniodes falcicornis |
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4 Crow louse Docophorus ocellatus |
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5 Pigeon louse Lipeurus baculus |
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6 Heron louse Liotheum importunum |
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7 Human body (or clothing) louse Pediculus vestimenti |
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8 Swan louse Ornithobius cygnorum |
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Lice are fascinating, ask any phthirapterist. Over 3,200 different louse species are known, infesting different mammals and birds around the globe.
Chewing lice infest birds, mostly, although some are found on cats, guinea-pigs, cattle, goats, horses and sheep. They have large, broad heads and chewing jaws with which to scrape skin. They usually have two claws at the end of each leg rather than one: maybe feathers need more clinging on to than hairs?
It is a marvellous mystery why Harrisoniella irroratae, the louse of the wandering albatross, has only four legs rather than the usual insect number of six. What should be its front pair are reduced to short stumps and instead it ‘walks’ by using its over-large antennae.
The pelican louse, Piagetiella titan, lives inside the bird’s peculiar beak. Every so often, however, it returns to the bird’s head to lay its eggs in the feathers.
Sucking lice have pointed blood-sucking mouthparts. Most mammals have at least one species of louse feeding on them. We humans have three. The exceptions are the carnivores, apart from the unfortunate dog, otter, seals, walrus and (by an odd quirk of evolutionary history and plate tectonics) marsupials.
Antarctophthirus ogmorhini, the louse of the Weddell seal has, perhaps, the hardest life of any insect. The seals spend most of their time in Antarctic seas, swimming in water at –2°C, and diving down to 450m for an hour at a time. The lice can barely hang on
The ‘snouted’ lice (only three species known) have their entire head extended into a giant pointed blood-sucking skewer. They have chosen to take their blood meals through the thick hide of elephants and warthogs. Respect!
