Human lice (Pediculus humanus) are world-wide, obligate, wingless ectoparasites that spend their full life cycle on humans; the medical term for the condition of being infested with lice is pediculosis. This species is comprised of two morphologically identical, interbreeding (at least in laboratory conditions, although not in natural ones), but behaviorally distinguishable subspecies that occupy non-overlapping habitats: Pediculus humanus corporis (human body lice; this subspecies is also known as Pediculus humanus humanus) and Pediculus humanus capitis (human head lice). As their names suggest, body lice are found hiding in and attaching their eggs to clothing, whereas head lice infest the host's scalp, and attach their eggs to the base of hairs. These subspecies are thought to have diverged about 110,000 years ago when humans started wearing clothing. Body lice infest mostly those living with poor hygiene and who do not have access to bathing facilities and clean sheets and clothes, as infestations do not persist through bathing and laundering. Body lice can carry such diseases as louse-borne typhus (Rickettsia prowazeki), trench fever (Rochalimaea quintana), and louse-borne relapsing fever (Borrellia recurrentis). Head lice, on the other hand, are not known to be disease vectors, but are a common and persistent nuisance of millions of people in the US alone, mainly school aged children.
(Morgan 2001; Smith; Wikipedia 2011a, 2011b)
- Head with distinctive dark eyes.
- Abdomen elongate and lacking distinct tubercles.
The head louse variant attaches eggs (nits) to the base of hair shafts, whereas body lice glue their eggs to projecting fibers of clothing on their host. Eggs typically hatch in 5 to 7 days and the nymphs reach maturity after a further 10 to 12 days.
Human lice can be found anywhere on the planet that is populated by humans. They are more prevalent in areas where people change or wash their clothing infrequently and/or are unclean themselves (Milne and Milne 1980).
Biogeographic Regions: nearctic (Native ); palearctic (Native ); oriental (Native ); ethiopian (Native ); neotropical (Native ); australian (Native ); oceanic islands (Native )
Other Geographic Terms: cosmopolitan
Pediculus humanus is a small insect with a large abdomen and legs equipped with sharp claws for holding onto hair and clothing fibers. The head of the louse ia slightly narrower than the body. They do not have wings like most insects, but they have piercing mouthparts for digging into the skin and draining out the blood. The head louse, Pediculus humanus capitis, is normally 1-2 mm long, while the body louse, Pediculus humanus humanus, also known as the "cootie" is usually slightly larger, 2-3.5 mm. The "nits," or eggs, of the louse are about 1 mm long and about half as wide. The young lice are often called "red backs," due to the red color they are because of the blood in them. They turn a grey color once digestion takes place, and is where they get the name "gray back".
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
- Grzimek, B. 1972. Animal Life Encyclopedia. New York: Van Nostrand Reinhold Company.
- Leftwich, A. 1977. A Dictionary of Entomology. New York: Crane Russak and Company, Inc..
- Milne, L., M. Milne. 1980. The Audubon Society Field Guide to North American Insects and Spiders. 1980: Alfred A. Knopf.
- Roberts, L., J. Janovy Jr.. 2000. Gerald D. Schmidt and Larry S. Roberts' Foundations of Parasitology, 6th Edition. Burr Ridge, Illinois, USA: McGraw Hill.
The habitat of the human louse is solely on the human body or in the clothes. They are rarely found elsewhere because they can only survive away from the host for a few days.
(Milne and Milne 1980)
Lice are obligate ectoparasites. They live off of the blood of humans. They have specially designed mouth parts for piercing the skin of humans and retrieving the blood that is present.
Animal Foods: blood
Primary Diet: carnivore (Sanguivore )
- Chew, A., S. Bashir, H. Maibach. 08/12/2000. Treatment of head lice. Lancet, 9229: 523-524.
egg (nit) of Pediculus humanus capitis lives on hair (head) of Homo sapiens
Other: sole host/prey
egg (nit) of Pediculus humanus humanus lives on clothing of Homo sapiens
Other: sole host/prey
Worldwide, living as an ectoparasite on humans but is also recorded from gibbons and New World monkeys.
Two morphological variants exist that were once thought to be separate species or subspecies. The form commonly referred to as “head lice” are restricted to the human scalp, while the form referred to as “body lice” are restricted to clothing and the human torso.
As a species, absolutely not endangered. However, populations restricted to isolated human tribes and non-human primates should be considered threatened.
Life History and Behavior
Feeding and diet
Both forms feed on blood. However, their ecology differs between body morphs. Head lice feed at regular intervals every few hours, whereas body lice feed only once or twice per day during periods of host inactivity.
The female lice lay their eggs, which are called nits, singly on the hairs of the host (if they are head lice) or attached to clothing in the case of body lice. The nits will hatch into nymphs in about eight days. The nymphs also suck blood and mature in eight to sixteen days. Each adult female body louse produces between two and three hundred nits in her lifetime, and a single female head louse produces between eighty and one-hundred. Due to this fact and that the generations follow at about three week intervals, a single female could inundate a host in a matter of months (Burton 1968, Grzimek 1972).
Molecular Biology and Genetics
Barcode data: Pediculus humanus
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Pediculus humanus
Public Records: 259
Specimens with Barcodes: 350
Species With Barcodes: 1
US Federal List: no special status
CITES: no special status
Relevance to Humans and Ecosystems
P. humanus has relatively little direct effect on its hosts. Bites itch, but do not generally cause other harm. However, lice can be vectors for important diseases. The three most important diseases they can carry are typhus, trench fever (both caused by bacteria in the genus Rickettsia), and relapsing fever (caused by another bacteria species Borrelia recurrentis). These bacterial diseases can now be treated successfully with antibiotics, but in the past, they caused the death of millions of people. Major epidemics strongly affected the political and economic history of Europe and Asia, and liice were the main agents in the spread of these diseases.
Lice cannot withstand high temperatures, so washing can eradicate the lice. Not until the practice of washing and changing our clothes on a regular basis have we been able to slow the spread of lice, and the diseases that they carry. In contrast to this, their occurrence increases greatly in time of war and hardship because people are closely packed and hygiene is not of high importance.
(Grzimek 1972; Roberts and Janovy 2000; Milne and Milne 1980)
The only way that this species could have any positive economic benefit would be to the people that are involved with selling the drugs and tools used to get rid of an infestation. Today, Lindane, permethrin, and malathion are used to kill the lice. Fine toothed combs are also used in a technique called wet combing, but this is usually accompanied with the use of one of the previously mentioned chemicals.
(Chew et. al. 2000)
Significance to humans
As the principal vector of epidemic typhus (Rickettsia prowazekii), the body louse variant is responsible for hundreds of millions of deaths up until the early nineteen hundreds. Since World War II, large outbreaks of typhus have occurred mainly in Africa, with reported cases coming predominantly from Burundi, Ethiopia and Rwanda.
The head louse variant is common in the western world, with infection rates exceeding 20% reported from selected primary schools in Australia, the UK and USA. However, this form is not known to transmit louse-borne diseases in natural circumstances.
- Pediculus humanus humanus Linnaeus, 1758 – the body louse
- Pediculus humanus capitis De Geer, 1767 – the head louse
- William H. Robinson (2005). "Phthiraptera". Handbook of Urban Insects and Arachnids. Cambridge University Press. pp. 359–364. ISBN 978-0-521-81253-5.
- Lance A. Durden & John E. Lloyd (2009). "Lice (Phthiraptera)". In Gary Mullen, Gary Richard Mullen & Lance Durden. Medical and Veterinary Entomology (2nd ed.). Academic Press. pp. 56–79. ISBN 978-0-12-372500-4.
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