Animal Diversity Web

Ge­o­graphic Range

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

Habi­tat

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)

Phys­i­cal De­scrip­tion

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". (Grz­imek, 1972; Left­wich, 1977; Milne and Milne, 1980; Roberts and Janovy Jr., 2000)

• Other Physical Features
• ectothermic
• heterothermic
• bilateral symmetry

Re­pro­duc­tion

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).

Be­hav­ior

There are very few mor­pho­log­i­cal dif­fer­ences be­tween the two sub-species. The main thing that keeps them sep­a­rated is their be­hav­ior. Body lice live and hide in the folds of the cloth­ing of the hosts, usu­ally close to the skin. They will nor­mally only crawl on the skin in order to feed. Head lice live on the scalp, ei­ther at­tached to the scalp while feed­ing or to the hairs.

The lice are trans­mit­ted from one per­son to an­other by di­rect con­tact, by clothes or a brush, or by fallen hair. Any­thing that has a nit or a fe­male on it will trans­mit the in­fes­ta­tion.

In the case of head lice, the fe­males are ac­tu­ally spe­cific about the part of the head where they lay their eggs. They pre­fer to lay them be­hind the ears or on the back of the head, near the neck line. (Grz­imek, 1972; Milne and Milne, 1980; Roberts and Janovy Jr., 2000)

• Key Behaviors
• parasite
• sedentary
• solitary

Food Habits

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. (Chew, et al., 08/12/2000; Left­wich, 1977)

• Primary Diet
• carnivore
  • sanguivore

• Animal Foods
• blood

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

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)

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

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)

Con­ser­va­tion Sta­tus

• IUCN Red List

  No special status

• US Federal List

  No special status

• CITES

  No special status

Con­trib­u­tors

Chris Mor­gan (au­thor), South­west­ern Uni­ver­sity, Stephanie Fab­ri­tius (ed­i­tor), South­west­ern Uni­ver­sity.

Ref­er­ences

Bur­ton, J. 1968. The Ox­ford Book of In­sects. Great Britain: Uni­ver­sity Press.

Chew, A., S. Bashir, H. Maibach. 08/12/2000. Treat­ment of head lice. Lancet, 9229: 523-524.

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.