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didae pachytroctidae sphaeropsocidae amphientometae psocomorpha homilopsocidea caeciliusetae psocetae epipsocetae philotarsetae archipsocetae trogiomorpha atropetae psyllipsocetae prionoglaridetae paraphyletic internal classification 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 9 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 10 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 6 7 also based on the paraphyletic nature of one of the parvorders ischnocera they recognised a fifth parvorder trichodectera which had been split off from ischnocera two years earlier here are the five proposed parvorders within phthiraptera 6 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 evolutionary history the oldest confirmed fossil louse is archimenopon myanmarensis an amblyceran from the cretaceous amber from myanmar 5 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 11 saurodectes vrsanskyi from the early cretaceous aptian zaza formation of buryatia russia has also been suggested to be a louse but this is tentative 12 placental mammal lice had a single common ancestor that lived on afrotheria with this arising from host switching from an ancient avian host 13 description 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 10 they are found even in the antarctic where penguins carry 15 species of lice in the genera austrogonoides and nesiotinus 14 ricinus bombycillae an amblyceran louse from a bohemian waxwing trinoton anserinum an amblyceran louse from a mute swan 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 15 if their host dies lice can opportunistically use phoresis to hitch a ride on a fly and attempt to find a new host 16 sucking lice range in length from 0 5 to 5 mm 1 64 to 13 64 in 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 17 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 18 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 17 chewing lice are also flattened and can be slightly larger than sucking lice ranging in length from 0 5 to 6 mm 1 64 to 15 64 in 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 17 19 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 15 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 15 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 20 ecology the average number of lice per host tends to be higher in large bodied bird species than in small ones 21 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 22 host organisms that dive under water to feed on aquatic prey harbour fewer taxa of lice 23 24 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 25 26 reductions in the size of host populations may cause a long lasting reduction of louse taxonomic richness 27 for example birds introduced into new zealand host fewer species of lice there than in europe 28 29 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 27 lice may reduce host life expectancy if the infestation is heavy 30 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 17 lice may transmit microbial diseases and helminth parasites 31 but most individuals spend their whole life cycle on a single host and are only able to transfer to a new host opportunistically 17 ischnoceran lice may reduce the thermoregulation effect of the plumage thus heavily infested birds lose more heat than others 32 lice infestation is a disadvantage in the context of sexual rivalry 33 34 reproduction most louse species reproduce sexually only a few parthenogenetic species are known they lay eggs also called nits after hatching they develop through three larval nymphal stages into adults imagoes their 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 35 their sex determination system is paternal genome elimination i e males are functionally haploid they appear to manipulate offspring sex ratios as predicted by hamilton s local mate competition hypothesis 36 in human culture for information about human infestation see pediculosis for information on treatment see treatment of human head lice in social history drawing of a louse clinging to a human hair robert hooke 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 37 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 38 a mediaeval treatment for lice was an ointment made from pork grease incense lead and aloe 39 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 40 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 41 42 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 43 despite this the modern view is that only the body louse can transmit the disease 44 detail showing delousing from jan siberechts 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 45 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 46 in literature and folklore mother louse a notorious alewife in oxford during the mid 18th century shown with three lice as a coat of arms image by david loggan 47 48 james joyce s 1939 book finnegans wake has the character shem the penman infested with foxtrotting fleas the lieabed lice bats in his belfry 49 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 50 the irish songwriter john lyons b 1934 wrote the popular 51 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 51 52 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 53 in science the human body louse pediculus humanus humanus has the smallest insect genome known 54 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 55 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 56 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 56 because parasites rely on their hosts host parasite cospeciation events are likely genetic evidence suggests that human ancestors acquired pubic lice from gorillas approximately 3 4 million years ago 56 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 host switch occurred in evolutionary history this explanation is the most parsimonious containing the fewest evolutionary changes 56 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 57 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 ...
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