louse

Lice are classified as an infraorder called Phthiraptera, named by Ernst Haeckel in 1896. Phthiraptera was previously recognized as an order, and was considered the sister taxon to the order Psocoptera, which contains booklice, barklice and barkflies, all within the greater group called Psocodea. However, a 2021 genetic study determined that Phthiraptera lice are a highly modified lineage within the Psocoptera group, thus rendering Psocoptera paraphyletic and necessating a classification change. Phthiraptera is now nested within the suborder Troctomorpha, belonging to the now-ranked order Psocodea.{{Cite journal|last1=de Moya|first1=Robert S|last2=Yoshizawa|first2=Kazunori|last3=Walden|first3=Kimberly K O|last4=Sweet|first4=Andrew D|last5=Dietrich|first5=Christopher H|last6=Kevin P|first6=Johnson|date=2021-06-16|editor-last=Buckley|editor-first=Thomas|title=Phylogenomics of Parasitic and Nonparasitic Lice (Insecta: Psocodea): Combining Sequence Data and Exploring Compositional Bias Solutions in Next Generation Data Sets|url=https://academic.oup.com/sysbio/article/70/4/719/5912026|journal=Systematic Biology|language=en|volume=70|issue=4|pages=719–738|doi=10.1093/sysbio/syaa075|pmid=32979270|issn=1063-5157|doi-access=free}}{{Cite web| website = Psocodea Species File |title = Anoplura Leach, 1815 |last1 = Hopkins |first1 = H. |last2 = Johnson |first2 = K. P. |last3 = Smith |first3 = V. S. |url = https://psocodea.speciesfile.org/otus/878997/overview |access-date = 12 May 2025 }} Within Psocodea, the Phthiraptera lice are most closely related to family Liposcelididae.{{cite journal | vauthors = Light JE, Smith VS, Allen JM, Durden LA, Reed DL | title = Evolutionary history of mammalian sucking lice (Phthiraptera: Anoplura) | journal = BMC Evolutionary Biology | volume = 10 | issue = 1 | pages = 292 | date = September 2010 | pmid = 20860811 | pmc = 2949877 | doi = 10.1186/1471-2148-10-292 | doi-access = free | bibcode = 2010BMCEE..10..292L }}

A cladogram showing the position of Phthiraptera within Psocodea is shown below:

{{clade| style=font-size:85%; line-height:100%

|label1=Psocodea

|1={{clade

|1={{clade

|label1=Troctomorpha

|1={{clade

|1={{clade

|1={{clade

|label1=Phthiraptera

|1={{clade

|1={{clade

|1=Philopteridae

|2={{clade

|1={{clade

|1=Anoplura

|2=Rhynchophthirina }}

|2=Trichodectidae }} }}

|2=Amblycera }}

|2=Liposcelididae }}

|2={{clade

|1=Pachytroctidae

|2=Sphaeropsocidae }} }}

|2=Amphientometae }}

|label2=Psocomorpha

|2={{clade

|1={{clade

|1={{clade

|1=Homilopsocidea

|2=Caeciliusetae }}

|2={{clade

|1={{clade

|1=Psocetae

|2=Epipsocetae }}

|2=Philotarsetae }} }}

|2=Archipsocetae }} }}

|label2=Trogiomorpha

|2={{clade

|1={{clade

|1=Atropetae

|2=Psyllipsocetae }}

|2=Prionoglaridetae (paraphyletic) }} }} }}

Phthiraptera is clearly a monophyletic grouping, united as the members are by a number of derived features, including their parasitism on warm-blooded vertebrates and the combination of their metathoracic ganglia with their abdominal ganglia to form a single ventral nerve junction.{{cite book| vauthors = Ax P |title=Multicellular Animals: Volume II: The Phylogenetic System of the Metazoa |url=https://books.google.com/books?id=x7vtCAAAQBAJ&pg=PA303 |year=2013|publisher=Springer Science & Business Media |isbn=978-3-662-10396-8 |pages=303–307 }}

The order has traditionally been divided into two suborders, the sucking lice (Anoplura) and the chewing lice (Mallophaga). However, subsequent classifications indicated that the Mallophaga are paraphyletic, and four suborders were then recognized.{{cite web |url=http://phthiraptera.info/ |title=Phthiraptera.info | vauthors = Smith V |publisher=International Society of Phthirapterists |access-date=25 October 2015}}

Upon finding that Phthiraptera was nested within Psocoptera in 2021, de Moya et al. reduced the rank of Phthiraptera to infraorder, and the suborders were reduced down to parvorder. Also, based on the paraphyletic nature of one of the parvorders - Ischnocera - they proposed creation of a fifth parvorder Trichodectera to be created and split off from Ischnocera. Here are the five proposed parvorders within Phthiraptera:

• Amblycera: primitive chewing lice, widespread on birds, and also occurring on South American and Australian mammals
• Anoplura: sucking lice, occurring on mammals exclusively
• Rhynchophthirina: parasites of elephants and warthogs
• Ischnocera: avian chewing lice, and contains the large family Philopteridae
• Trichodectera: parasitizing mammals, split off from Ischnocera, and contains the family Trichodectidae

The oldest confirmed fossil louse is Archimenopon myanmarensis, an amblyceran from the Cretaceous amber from Myanmar. Another early representative of the group is a bird louse, Megamenopon rasnitsyni, from Eckfelder Maar, Germany, which dates to the Eocene, around 44 million years ago.{{cite journal | vauthors = Wappler T, Smith VS, Dalgleish RC | title = Scratching an ancient itch: an Eocene bird louse fossil | journal = Proceedings. Biological Sciences | volume = 271 Suppl 5 | issue = suppl_5 | pages = S255-8 | date = August 2004 | pmid = 15503987 | pmc = 1810061 | doi = 10.1098/rsbl.2003.0158 }} Saurodectes vrsanskyi from the Early Cretaceous (Aptian) Zaza Formation of Buryatia, Russia, has also been suggested to be a louse, but this is tentative.{{cite journal | vauthors = Rasnitsyn AP, Zherikhin VV | title = First fossil chewing louse from the lower Cretaceous of Baissa, Transbaikalia (Insecta, Pediculida= Phthiriaptera, Saurodectidae fam. n.). | journal = Russian Entomological Journal | date = 1999 | volume = 8 | issue = 4 | pages = 253–5 }}

Placental mammal lice had a single common ancestor that lived on Afrotheria with this arising from host-switching from an ancient avian host.{{cite journal |last1=Johnson |first1=Kevin P. |last2=Matthee |first2=Conrad |last3=Doña |first3=Jorge |date=2022 |title=Phylogenomics reveals the origin of mammal lice out of Afrotheria |journal=Nature Ecology & Evolution |volume=6 |issue=8 |pages=1205–1210 |doi=10.1038/s41559-022-01803-1 |pmid=35788706 |bibcode=2022NatEE...6.1205J |issn=2397-334X}}

Nearly 5,000 species of louse have been identified, about 4,000 being parasitic on birds and 800 on mammals. Lice are present on every continent in all the habitats that their host animals occupy. They are found even in the Antarctic, where penguins carry 15 species of lice (in the genera Austrogonoides and Nesiotinus).{{cite journal | vauthors = Banks JC, Paterson AM |title=A penguin-chewing louse (Insecta : Phthiraptera) phylogeny derived from morphology |journal=Invertebrate Systematics |date=2004 |volume=18 |issue=1 |pages=89–100 |doi=10.1071/IS03022 |s2cid=53516244 }}

File:Ricinus bombycillae (Denny, 1842).JPG|Ricinus bombycillae, an amblyceran louse from a Bohemian waxwing

File:Trinoton anserinum (Fabricius, 1805).JPG|Trinoton anserinum, an amblyceran louse from a mute swan

File:Lice image01.jpg|Bovicola limbata, an ischnoceran louse from goats. The species is sexually dimorphic, with the male smaller than the female.

Lice are divided into two groups: sucking lice, which obtain their nourishment from feeding on the sebaceous secretions and body fluids of their host; and chewing lice, which are scavengers, feeding on skin, fragments of feathers or hair, and debris found on the host's body. Many lice are specific to a single species of host and have co-evolved with it. In some cases, they live on only a particular part of the body. Some animals are known to host up to fifteen different species, although one to three is typical for mammals, and two to six for birds. Lice generally cannot survive for long if removed from their host.{{cite book | vauthors = Hoell HV, Doyen JT, Purcell AH |year=1998 |title=Introduction to Insect Biology and Diversity |edition=2nd |publisher= Oxford University Press |pages= 407–409|isbn= 978-0-19-510033-4}} If their host dies, lice can opportunistically use phoresis to hitch a ride on a fly and attempt to find a new host.{{cite thesis | vauthors = Harbison CW | date = 2008 |title=Ecology and Evolution of Transmission in Feather-feeding Lice (Phthiraptera: Ischnocera) | degree = Doctoral | work = Department of Biology | publisher = University of Utah |url=https://books.google.com/books?id=RUfFjqPoQTEC&pg=PA83 |isbn=978-0-549-46429-7 |pages=83–87}}

Sucking lice range in length from {{convert|0.5|to|5|mm|in|frac=64|abbr=on}}. They have narrow heads and oval, flattened bodies. They have no ocelli, and their compound eyes are reduced in size or absent. Their antennae are short with three to five segments, and their mouthparts, which are retractable into their head, are adapted for piercing and sucking. There is a cibarial pump at the start of the gut; it is powered by muscles attached to the inside of the cuticle of the head. The mouthparts consist of a proboscis which is toothed, and a set of stylets arranged in a cylinder inside the proboscis, containing a salivary canal (ventrally) and a food canal (dorsally).{{cite book| vauthors = Gullan PJ, Cranston PS |title=The Insects: An Outline of Entomology |date=2014 |publisher=Wiley |isbn=978-1-118-84615-5 |pages=41–42}} The thoracic segments are fused, the abdominal segments are separate, and there is a single large claw at the tip of each of the six legs.{{cite book| vauthors = Capinera JL |title=Encyclopedia of Entomology |url=https://books.google.com/books?id=i9ITMiiohVQC&pg=PA838 |year=2008 |publisher=Springer Science & Business Media |isbn=978-1-4020-6242-1 |pages=838–844}}

Chewing lice are also flattened and can be slightly larger than sucking lice, ranging in length from {{convert|0.5|to|6|mm|in|frac=64|abbr=on}}. They are similar to sucking lice in form but the head is wider than the thorax and all species have compound eyes. There are no ocelli and the mouthparts are adapted for chewing. The antennae have three to five segments and are slender in the suborder Ischnocera, but club-shaped in the suborder Amblycera. The legs are short and robust, and terminated by one or two claws. Some species of chewing lice house symbiotic bacteria in bacteriocytes in their bodies. These may assist in digestion because if the insect is deprived of them, it will die.

Lice are usually cryptically coloured to match the fur or feathers of the host.{{cite web |url=http://phthiraptera.info/classification/23 |title=Phthiraptera: Summary |vauthors=Smith V |publisher=Phthiraptera.info |access-date=25 October 2015 }}{{Dead link|date=August 2023 |bot=InternetArchiveBot |fix-attempted=yes }} A louse's colour varies from pale beige to dark grey; however, if feeding on blood, it may become considerably darker.

Female lice are usually more common than males, and some species are parthenogenetic, with young developing from unfertilized eggs. A louse's egg is commonly called a nit. Many lice attach their eggs to their hosts' hair with specialized saliva; the saliva/hair bond is very difficult to sever without specialized products. Lice inhabiting birds, however, may simply leave their eggs in parts of the body inaccessible to preening, such as the interior of feather shafts. Living louse eggs tend to be pale whitish, whereas dead louse eggs are yellower. Lice are exopterygotes, being born as miniature versions of the adult, known as nymphs. The young moult three times before reaching the final adult form, usually within a month after hatching.

Humans host three different kinds of lice: head lice, body lice, and pubic lice. Head lice and body lice are subspecies of Pediculus humanus, and pubic lice are a separate species, Pthirus pubis. Lice infestations can be controlled with lice combs, and medicated shampoos or washes.{{cite journal | vauthors = Mumcuoglu KY | title = Prevention and treatment of head lice in children | journal = Paediatric Drugs | volume = 1 | issue = 3 | pages = 211–8 | year = 1999 | pmid = 10937452 | doi = 10.2165/00128072-199901030-00005 | s2cid = 13547569 }}

The average number of lice per host tends to be higher in large-bodied bird species than in small ones.{{cite journal | vauthors = Rózsa | year = 1997| title = Patterns in the abundance of avian lice (Phthiraptera: Amblycera, Ischnocera) | url = http://www.zoologia.hu/list/patterns%20in%20the%20abundance.pdf | journal = Journal of Avian Biology | volume = 28 | issue = 3| pages = 249–254 | doi=10.2307/3676976| jstor = 3676976}} Lice have an aggregated distribution across bird individuals, i.e. most lice live on a few birds, while most birds are relatively free of lice. This pattern is more pronounced in territorial than in colonial—more social—bird species.{{cite journal | vauthors = Rékási J, Rozsa L, Kiss BJ | year = 1997 | title = Patterns in the distribution of avian lice (Phthiraptera: Amblycera, Ischnocera) | url = http://www.zoologia.hu/list/patterns%20in%20the%20distribution.pdf | journal = Journal of Avian Biology | volume = 28 | issue = 2| pages = 150–156 | doi=10.2307/3677308 | jstor = 3677308 | citeseerx = 10.1.1.506.730 }} Host organisms that dive under water to feed on aquatic prey harbour fewer taxa of lice.{{cite journal | vauthors = Felsõ B, Rózsa L | title = Reduced taxonomic richness of lice (Insecta: Phthiraptera) in diving birds | journal = The Journal of Parasitology | volume = 92 | issue = 4 | pages = 867–9 | date = August 2006 | pmid = 16995408 | doi = 10.1645/ge-849.1 | s2cid = 31000581 }}{{cite journal | vauthors = Felső B, Rózsa L | year = 2007 | title = Diving behaviour reduces genera richness of lice (Insecta: Phthiraptera) of mammals | url = http://www.zoologia.hu/list/felso_rozsa2.pdf | journal = Acta Parasitologica | volume = 52 | pages = 82–85 | doi=10.2478/s11686-007-0006-3| s2cid = 38683871 }} Bird taxa that are capable of exerting stronger antiparasitic defence—such as stronger T cell immune response or larger uropygial glands—harbour more taxa of Amblyceran lice than others.{{cite journal | vauthors = Møller AP, Rózsa L | title = Parasite biodiversity and host defenses: chewing lice and immune response of their avian hosts | journal = Oecologia | volume = 142 | issue = 2 | pages = 169–76 | date = January 2005 | pmid = 15503162 | doi = 10.1007/s00442-004-1735-8 | s2cid = 12992951 | bibcode = 2005Oecol.142..169M }}{{cite journal | vauthors = Møller AP, Erritzøe J, Rózsa L | title = Ectoparasites, uropygial glands and hatching success in birds | journal = Oecologia | volume = 163 | issue = 2 | pages = 303–11 | date = June 2010 | pmid = 20043177 | doi = 10.1007/s00442-009-1548-x | s2cid = 11433594 | bibcode = 2010Oecol.163..303M }} Reductions in the size of host populations may cause a long-lasting reduction of louse taxonomic richness,{{cite journal | vauthors = Ròzsa L | title = Speciation patterns of ectoparasites and "straggling" lice | journal = International Journal for Parasitology | volume = 23 | issue = 7 | pages = 859–64 | date = November 1993 | pmid = 8314369 | doi = 10.1016/0020-7519(93)90050-9 }} for example, birds introduced into New Zealand host fewer species of lice there than in Europe.{{cite journal | vauthors = Paterson AM, Palma RL, Gray RD | year = 1999 | title = How Frequently Do Avian Lice Miss the Boat? Implications for Coevolutionary Studies | journal = Systematic Biology | volume = 48 | pages = 214–223 | doi=10.1080/106351599260544 | doi-access = free }}{{cite journal | vauthors = MacLeod CJ, Paterson AM, Tompkins DM, Duncan RP | title = Parasites lost - do invaders miss the boat or drown on arrival? | journal = Ecology Letters | volume = 13 | issue = 4 | pages = 516–27 | date = April 2010 | pmid = 20455925 | doi = 10.1111/j.1461-0248.2010.01446.x | bibcode = 2010EcolL..13..516M }} Louse sex ratios are more balanced in more social hosts and more female-biased in less social hosts, presumably due to the stronger isolation among louse subpopulations (living on separate birds) in the latter case.{{cite journal | vauthors = Rózsa L, Rékási J, Reiczigel J | year = 1996 | title = Relationship of host coloniality to the population ecology of avian lice (Insecta: Phthiraptera) | url = http://www.zoologia.hu/list/relationship%20of%20host%20coloniality.pdf | journal = Journal of Animal Ecology | volume = 65 | issue = 2| pages = 242–248 | doi=10.2307/5727 | jstor = 5727 | bibcode = 1996JAnEc..65..242R }} The extinction of a species results in the extinction of its host-specific lice. Host-switching is a random event that would seem very rarely likely to be successful, but speciation has occurred over evolutionary time-scales so it must be successfully accomplished sometimes.

Lice may reduce host life expectancy if the infestation is heavy,{{cite journal | vauthors = Brown CR, Brown MB, Rannala B | year = 1995 | title = Ectoparasites reduce long-term survivorship of their avian host | url = http://www.rannala.org/reprints/1995/Brown1995a.pdf | journal = Proceedings of the Royal Society of London B | volume = 262 | issue = 1365| pages = 313–319 | doi=10.1098/rspb.1995.0211| s2cid = 13869042 }} but most seem to have little effect on their host. The habit of dust bathing in domestic hens is probably an attempt by the birds to rid themselves of lice. Lice may transmit microbial diseases and helminth parasites,{{cite journal | vauthors = Barlett CM |year=1993 |title=Lice (Amblycera and Ischnocera) as vectors of Eulimdana spp. (Nematoda: Filarioidea) in Charadriiform birds and the necessity of short reproductive periods in adult worms |journal=Journal of Parasitology |volume=75 |issue=1 |pages=85–91 |jstor=3283282 |doi=10.2307/3283282}} but most individuals spend their whole life cycle on a single host and are only able to transfer to a new host opportunistically. Ischnoceran lice may reduce the thermoregulation effect of the plumage; thus heavily infested birds lose more heat than others.{{cite journal | vauthors = Booth DT, Clayton DH, Block BA | year = 1993 | title = Experimental demonstration of the energetic cost of parasitism in free-ranging hosts | url = http://darwin.biology.utah.edu/PubsHTML/PDF-Files/18.pdf | journal = Proceedings of the Royal Society of London B | volume = 253 | issue = 1337 | pages = 125–129 | doi = 10.1098/rspb.1993.0091 | bibcode = 1993RSPSB.253..125B | s2cid = 85731062 | access-date = 2010-08-14 | archive-url = https://web.archive.org/web/20100610162227/http://darwin.biology.utah.edu/PubsHTML/PDF-Files/18.pdf | archive-date = 2010-06-10 | url-status = dead }} Lice infestation is a disadvantage in the context of sexual rivalry.{{cite journal | vauthors = Clayton | year = 1990 | title = Mate choice in experimentally parasitized rock doves: lousy males lose | url = http://darwin.biology.utah.edu/PubsHTML/PDF-Files/11.pdf | journal = American Zoologist | volume = 30 | issue = 2 | pages = 251–262 | doi = 10.1093/icb/30.2.251 | access-date = 2010-08-14 | archive-url = https://web.archive.org/web/20100610164747/http://darwin.biology.utah.edu/PubsHTML/PDF-Files/11.pdf | archive-date = 2010-06-10 | url-status = dead | doi-access = free }}{{cite journal | vauthors = Garamszegi LZ, Heylen D, Møller AP, Eens M, De Lope F | year = 2005 | title = Age-dependent health status and song characteristics | journal = Behavioral Ecology | volume = 16 | issue = 3| pages = 580–591 | doi=10.1093/beheco/ari029 | doi-access = free }}

{{About||information about human infestation|Pediculosis|information on treatment|Treatment of human head lice}}

File:Louse diagram, Micrographia, Robert Hooke, 1667.jpg, Micrographia, 1667]]

Lice have been intimately associated with human society throughout history. In the Middle Ages, they were essentially ubiquitous. At the death of Thomas Becket, Archbishop of Canterbury in 1170, it was recorded that "The vermin boiled over like water in a simmering cauldron, and the onlookers burst into alternate weeping and laughing".{{cite journal | vauthors = Kowalski TJ, Agger WA | title = Art supports new plague science | journal = Clinical Infectious Diseases | volume = 48 | issue = 1 | pages = 137–8 | date = January 2009 | pmid = 19067623 | doi = 10.1086/595557 | doi-access = free }} The clergy often saw lice and other parasites as a constant reminder of human frailty and weakness. Monks and nuns would purposely ignore grooming themselves and suffer from infestations to express their religious devotion.{{Cite web |last=Harvey |first=Katherine |date=2019-04-09 |title=Medieval people were surprisingly clean (apart from the clergy) |url=https://aeon.co/essays/medieval-people-were-surprisingly-clean-apart-from-the-clergy |access-date=2022-10-13 |website=Aeon |language=en}} A mediaeval treatment for lice was an ointment made from pork grease, incense, lead, and aloe.{{cite book | vauthors = Elliott L |title=Clothing in the Middle Ages |url=https://books.google.com/books?id=qtq_WSpdo0gC&pg=PT29 |year=2004 |publisher=Crabtree |isbn=978-0-7787-1351-7 |page=29}}

Robert Hooke's 1667 book, Micrographia: or some physiological descriptions of minute bodies made by magnifying glasses with observations and Inquiries thereupon, illustrated a human louse, drawn as seen down an early microscope.{{cite web | vauthors = Hooke R |title=Microscopic view of a louse |url=http://prints.royalsociety.org/art/580831/microscopic-view-of-a-louse |publisher=The Royal Society |access-date=17 October 2015}}

Margaret Cavendish's satirical The Description of a New World, Called The Blazing-World (1668) has "Lice-men" as "mathematicians", investigating nature by trying to weigh the air like the real scientist Robert Boyle.{{cite book | vauthors = Sarasohn LT |title=The Natural Philosophy of Margaret Cavendish: Reason and Fancy During the Scientific Revolution |url=https://books.google.com/books?id=sE0XnNgF9ZoC&pg=PA167 |year=2010 |publisher=JHU Press |isbn=978-0-8018-9443-5|pages=165–167 |quote=The Bear-men were to be her Experimental Philosophers, the Bird-men her Astronomers, the Fly- Worm- and Fish-men her Natural Philosophers, the Ape-men her Chymists, the Satyrs her Galenick Physicians, the Fox-men her Politicians, the Spider- and Lice-men her Mathematicians, the Jackdaw- Magpie- and Parrot-men her Orators and Logicians, the Gyants her Architects, &c.}}{{cite book| vauthors = Cavendish M |title=The Description of a New World, Called the Blazing-World|date=1668|publisher=A. Maxwell|url=http://digital.library.upenn.edu/women/newcastle/blazing/blazing.html}}

In 1935 the Harvard medical researcher Hans Zinsser wrote the book Rats, Lice and History, alleging that both body and head lice transmit typhus between humans.{{cite book | vauthors = Zinsser H |title=Rats, Lice and History |date=2007 |orig-year=1935 |publisher=Transaction Publishers |isbn=978-1-4128-0672-5}} Despite this, the modern view is that only the body louse can transmit the disease.{{cite web | vauthors = Altschuler DZ |title=Zinsser, Lice and History |url=http://www.headlice.org/faq/disease/zinsser.htm |publisher=HeadLice.org |access-date=19 October 2015 |date=1990}}

File:Jan Siberechts "Cour de ferme" détail Scène d'épouillage.jpg' painting Cour de ferme ("Farmyard"), 1662]]

Soldiers in the trenches of the First World War suffered severely from lice, and the typhus they carried. The Germans boasted that they had lice under effective control, but themselves suffered badly from lice in the Second World War on the Eastern Front, especially in the Battle of Stalingrad. "Delousing" became a euphemism for the extermination of Jews in concentration camps such as Auschwitz under the Nazi regime.{{cite web | vauthors = Evans RJ |author-link1=Richard J. Evans |title=The Great Unwashed |url=http://www.gresham.ac.uk/lectures-and-events/the-great-unwashed |publisher=Gresham College |access-date=17 October 2015}}

In the psychiatric disorder delusional parasitosis, patients express a persistent irrational fear of animals such as lice and mites, imagining that they are continually infested and complaining of itching, with "an unshakable false belief that live organisms are present in the skin".{{cite web | vauthors = Weinstein P | date = 26 February 2013 | title = 'The Great Unwashed': Entomophobia/Delusionary Parasitosis; Illusionary Parasitosis | url = http://medent.usyd.edu.au/fact/delpara.htm | publisher = University of Sydney Department of Medical Entomology | access-date = 17 October 2015 | series = The Great Plagues: Epidemics in History from the Middle Ages to the Present Day | archive-date = 17 May 2016 | archive-url = https://web.archive.org/web/20160517005233/http://medent.usyd.edu.au/fact/delpara.htm | url-status = dead }}

File:Mother Louse, Alewife Wellcome L0000658.jpg in Oxford during the mid-18th century, shown with three lice as a coat of arms. Image by David Loggan.{{cite book|url=https://books.google.com/books?id=l68ZhT2agbEC&pg=PA275|title=Notes & Queries|publisher=Oxford University Press|year=1859|pages=275–276| vauthors = White W }}{{Cite web|publisher=University of York| vauthors = Pierce H |title=Unseemly pictures: political graphic satire in England, c. 1600-c. 1650|date=2004|url=http://etheses.whiterose.ac.uk/9864/1/423697_vol1.pdf}}]]

James Joyce's 1939 book Finnegans Wake has the character Shem the Penman infested with "foxtrotting fleas, the lieabed lice, ... bats in his belfry".{{cite book | vauthors = Joyce J | author-link1 = James Joyce |title=Finnegans Wake |date=1939 |publisher=Faber |page=180}}

Clifford E. Trafzer's A Chemehuevi Song: The Resilience of a Southern Paiute Tribe retells the story of Sinawavi (Coyote)'s love for Poowavi (Louse). Her eggs are sealed in a basket woven by her mother, who gives it to Coyote, instructing him not to open it before he reaches home. Hearing voices coming from it, however, Coyote opens the basket and the people, the world's first human beings, pour out of it in all directions.{{cite book | vauthors = Trafzer CE |title=A Chemehuevi Song: The Resilience of a Southern Paiute Tribe |url=https://books.google.com/books?id=GA81CgAAQBAJ&pg=PA24 |date=2015 |publisher=University of Washington Press |isbn=978-0-295-80582-5 |pages=22–25}}

The Irish songwriter John Lyons (b. 1934) wrote the popular song The Kilkenny Louse House. The song contains the lines "Well we went up the stairs and we put out the light, Sure in less than five minutes, I had to show fight. For the fleas and the bugs they collected to march, And over me stomach they formed a great arch". It has been recorded by Christie Purcell (1952), Mary Delaney on From Puck to Appleby (2003), and the Dubliners on Double Dubliners (1972) among others.{{cite web | vauthors = Carroll J |title=Songs of Clare: The Kilkenny Louse House |url=http://www.clarelibrary.ie/eolas/coclare/songs/cmc/the_kilkenny_louse_house_jlyons.htm |publisher=Clare Library |access-date=19 October 2015}}{{cite web |vauthors=Scott B |title=My Colleen by the Shore |url=http://www.veteran.co.uk/VT149CD%20Paginated%20booklet%20pages.pdf |publisher=Veteran |year=2013 |access-date=25 October 2015 |archive-date=4 March 2016 |archive-url=https://web.archive.org/web/20160304000329/http://www.veteran.co.uk/VT149CD%20Paginated%20booklet%20pages.pdf |url-status=dead }}

Robert Burns dedicated a poem to the louse, inspired by witnessing one on a lady's bonnet in church: "Ye ugly, creepin, blastid wonner, Detested, shunn'd, by saint and sinner, How dare ye set your fit upon her, sae fine lady! Gae somewhere else, and seek your dinner on some poor body." John Milton in Paradise Lost mentioned the biblical plague of lice visited upon pharaoh: "Frogs, lice, and flies must all his palace fill with loathed intrusion, and filled all the land." John Ray recorded a Scottish proverb, "Gie a beggar a bed and he'll repay you with a Louse." In Shakespeare's Troilus and Cressida, Thersites compares Menelaus, brother of Agamemnon, to a louse: "Ask me not what I would be, if I were not Thersites; for I care not to be the louse of a lazar, so I were not Menelaus."{{Cite thesis |title=Insect Life in the Poetry and Drama of England: With Special Reference to Poetry | vauthors = Twinn CR |publisher=University of Ottawa | degree= PhD |year=1942 |hdl=10393/21088 }}

The human body louse Pediculus humanus humanus has the smallest insect genome known,{{cite journal | vauthors = Kirkness EF, Haas BJ, Sun W, Braig HR, Perotti MA, Clark JM, Lee SH, Robertson HM, Kennedy RC, Elhaik E, Gerlach D, Kriventseva EV, Elsik CG, Graur D, Hill CA, Veenstra JA, Walenz B, Tubío JM, Ribeiro JM, Rozas J, Johnston JS, Reese JT, Popadic A, Tojo M, Raoult D, Reed DL, Tomoyasu Y, Kraus E, Krause E, Mittapalli O, Margam VM, Li HM, Meyer JM, Johnson RM, Romero-Severson J, Vanzee JP, Alvarez-Ponce D, Vieira FG, Aguadé M, Guirao-Rico S, Anzola JM, Yoon KS, Strycharz JP, Unger MF, Christley S, Lobo NF, Seufferheld MJ, Wang N, Dasch GA, Struchiner CJ, Madey G, Hannick LI, Bidwell S, Joardar V, Caler E, Shao R, Barker SC, Cameron S, Bruggner RV, Regier A, Johnson J, Viswanathan L, Utterback TR, Sutton GG, Lawson D, Waterhouse RM, Venter JC, Strausberg RL, Berenbaum MR, Collins FH, Zdobnov EM, Pittendrigh BR | display-authors = 6 | title = Genome sequences of the human body louse and its primary endosymbiont provide insights into the permanent parasitic lifestyle | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 107 | issue = 27 | pages = 12168–73 | date = July 2010 | pmid = 20566863 | pmc = 2901460 | doi = 10.1073/pnas.1003379107 | bibcode = 2010PNAS..10712168K | doi-access = free }} and this louse can transmit certain diseases that the closely related human head louse (P. h. capitis) cannot. With their simple life history and small genomes, the pair make ideal model organisms to study the molecular mechanisms behind the transmission of pathogens and vector competence.{{cite journal | vauthors = Pittendrigh BR, Berenbaum MR, Seufferheld MJ, Margam VM, Strycharz JP, Yoon KS, Sun W, Reenan R, Lee SH, Clark JM | display-authors = 6 | title = Simplify, simplify: Lifestyle and compact genome of the body louse provide a unique functional genomics opportunity | journal = Communicative & Integrative Biology | volume = 4 | issue = 2 | pages = 188–91 | date = March 2011 | pmid = 21655436 | pmc = 3104575 | doi = 10.4161/cib.4.2.14279 }}

Lice have been the subject of significant DNA research in the 2000s that led to discoveries on human evolution. The three species of sucking lice that parasitize human beings belong to two genera, Pediculus and Pthirus: head lice (Pediculus humanus capitis), body lice (Pediculus humanus humanus), and pubic lice (Pthirus pubis). Human head and body lice (genus Pediculus) share a common ancestor with chimpanzee lice, while pubic lice (genus Pthirus) share a common ancestor with gorilla lice. Using phylogenetic and cophylogenetic analysis, Reed et al. hypothesized that Pediculus and Pthirus are sister taxa and monophyletic. In other words, the two genera descended from the same common ancestor. The age of divergence between Pediculus and its common ancestor is estimated to be 6-7 million years ago, which matches the age predicted by chimpanzee-hominid divergence. Because parasites rely on their hosts, host{{endash}}parasite cospeciation events are likely.

Genetic evidence suggests that human ancestors acquired pubic lice from gorillas approximately 3-4 million years ago.{{cite journal | vauthors = Reed DL, Light JE, Allen JM, Kirchman JJ | title = Pair of lice lost or parasites regained: the evolutionary history of anthropoid primate lice | journal = BMC Biology | volume = 5 | issue = 7 | pages = 7 | date = March 2007 | pmid = 17343749 | pmc = 1828715 | doi = 10.1186/1741-7007-5-7 | doi-access = free }} Unlike the genus Pediculus, the divergence in Pthirus does not match the age of host divergence that likely occurred 7 million years ago. Reed et al. propose a Pthirus species host-switch around 3-4 million years ago. While it is difficult to determine if a parasite{{endash}}host switch occurred in evolutionary history, this explanation is the most parsimonious (containing the fewest evolutionary changes).

Additionally, the DNA differences between head lice and body lice provide corroborating evidence that humans used clothing between 80,000 and 170,000 years ago, before leaving Africa.{{cite web | vauthors = Parry W |title=Lice Reveal Clues to Human Evolution |url=http://www.livescience.com/41028-lice-reveal-clues-to-human-evolution.html |publisher=LiveScience |access-date=25 October 2015 |date=7 November 2013}} Human head and body lice occupy distinct ecological zones: head lice live and feed on the scalp, while body lice live on clothing and feed on the body. Because body lice require clothing to survive, the divergence of head and body lice from their common ancestor provides an estimate of the date of introduction of clothing in human evolutionary history.{{cite journal | vauthors = Kittler R, Kayser M, Stoneking M | title = Molecular evolution of Pediculus humanus and the origin of clothing | journal = Current Biology | volume = 13 | issue = 16 | pages = 1414–7 | date = August 2003 | pmid = 12932325 | doi = 10.1016/S0960-9822(03)00507-4 | s2cid = 15277254 | doi-access = free | bibcode = 2003CBio...13.1414K }}

The mitochondrial genome of the human species of the body louse (Pediculus humanus humanus), the head louse (Pediculus humanus capitis) and the pubic louse (Pthirus pubis) fragmented into a number of minichromosomes at least seven million years ago.{{cite journal | vauthors = Shao R, Zhu XQ, Barker SC, Herd K | title = Evolution of extensively fragmented mitochondrial genomes in the lice of humans | journal = Genome Biology and Evolution | volume = 4 | issue = 11 | pages = 1088–101 | year = 2012 | pmid = 23042553 | pmc = 3514963 | doi = 10.1093/gbe/evs088 }} Analysis of mitochondrial DNA in human body and hair lice reveals that greater genetic diversity existed in African than in non-African lice.{{cite journal | vauthors = Light JE, Allen JM, Long LM, Carter TE, Barrow L, Suren G, Raoult D, Reed DL | display-authors = 6 | title = Geographic distributions and origins of human head lice (Pediculus humanus capitis) based on mitochondrial data | journal = The Journal of Parasitology | volume = 94 | issue = 6 | pages = 1275–81 | date = December 2008 | pmid = 18576877 | doi = 10.1645/GE-1618.1 | s2cid = 9456340 }} Human lice can also shed light on human migratory patterns in prehistory. The dominating theory of anthropologists regarding human migration is the Out of Africa Hypothesis. Genetic diversity accumulates over time, and mutations occur at a relatively constant rate. Because there is more genetic diversity in African lice, the lice and their human hosts must have existed in Africa before anywhere else.

The name woodlouse or wood-louse is given to crustaceans of the suborder Oniscidea within the order Isopoda, unrelated to lice. The Oxford English Dictionary{{'}}s earliest citation of this usage is from 1611.{{Cite OED|Woodlouse}}

• Pest (organism)
• Use of DNA in forensic entomology

{{Reflist}}

{{Commons category|Phthiraptera}}

{{Wikispecies|Phthiraptera}}

{{Wiktionary|louse}}

• [http://npic.orst.edu/pest/lice.html National Pesticide Information Center – Understanding and Controlling Lice]
• [http://entomology.ifas.ufl.edu/creatures/urban/human_lice.htm body and head lice] on the University of Florida/Institute of Food and Agricultural Sciences Featured Creatures Web site
• [http://entomology.ifas.ufl.edu/creatures/urban/crab_louse.htm crab louse] on the University of Florida/Institute of Food and Agricultural Sciences Featured Creatures Web site
• [https://web.archive.org/web/20150715200253/http://www.metapathogen.com/lice/phumanus/ Pediculus humanus capitis head louse facts, myths, life cycle at MetaPathogen]
• [https://en.wikibooks.org/wiki/Parasitic_Insects,_Mites_and_Ticks:_Genera_of_Medical_and_Veterinary_Importance/Sucking_lice Parasitic Insects, Mites and Ticks: Genera of Medical and Veterinary Importance] Wikibooks

{{Human lice}}

{{Psocodea|2}}

{{Insects in culture}}

{{Taxonbar|from=Q6481228}}

{{Authority control}}

Category:Insects in culture

Category:Taxa named by Ernst Haeckel

Category:Delusional parasitosis

Category:Nanopsocetae