50-556: Louse ( pl. : lice ) is the common name for any member of the clade Phthiraptera , which contains nearly 5,000 species of wingless parasitic insects . Phthiraptera has variously been recognized as an order , infraorder , or a parvorder , as a result of developments in phylogenetic research. Lice are obligate parasites , living externally on warm-blooded hosts which include every species of bird and mammal , except for monotremes , pangolins , and bats . Lice are vectors of diseases such as typhus . Chewing lice live among
100-565: 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). 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. Human head and body lice occupy distinct ecological zones: head lice live and feed on
150-662: A model organism and has been the subject of much research. Lice were ubiquitous in human society until at least the Middle Ages . They appear in folktales, songs such as The Kilkenny Louse House , and novels such as James Joyce 's Finnegans Wake . They commonly feature in the psychiatric disorder delusional parasitosis . A louse was one of the early subjects of microscopy , appearing in Robert Hooke 's 1667 book, Micrographia . Lice are divided into two groups: sucking lice, which obtain their nourishment from feeding on
200-442: 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. The order has traditionally been divided into two suborders, the sucking lice (Anoplura) and the chewing lice (Mallophaga); however, subsequent classifications suggest that
250-717: A phylogenetic tree . In the taxonomical literature, sometimes the Latin form cladus (plural cladi ) is used rather than the English form. Clades are the fundamental unit of cladistics , a modern approach to taxonomy adopted by most biological fields. The common ancestor may be an individual, a population , or a species ( extinct or extant ). Clades are nested, one in another, as each branch in turn splits into smaller branches. These splits reflect evolutionary history as populations diverged and evolved independently. Clades are termed monophyletic (Greek: "one clan") groups. Over
300-479: A "ladder", with supposedly more "advanced" organisms at the top. Taxonomists have increasingly worked to make the taxonomic system reflect evolution. When it comes to naming , this principle is not always compatible with the traditional rank-based nomenclature (in which only taxa associated with a rank can be named) because not enough ranks exist to name a long series of nested clades. For these and other reasons, phylogenetic nomenclature has been developed; it
350-623: A clade can be described based on two different reference points, crown age and stem age. The crown age of a clade refers to the age of the most recent common ancestor of all of the species in the clade. The stem age of a clade refers to the time that the ancestral lineage of the clade diverged from its sister clade. A clade's stem age is either the same as or older than its crown age. Ages of clades cannot be directly observed. They are inferred, either from stratigraphy of fossils , or from molecular clock estimates. Viruses , and particularly RNA viruses form clades. These are useful in tracking
400-449: 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
450-442: 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. Host organisms that dive under water to feed on aquatic prey harbour fewer taxa of lice. 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. Reductions in
500-469: A highly modified lineage of Psocoptera (now called Psocodea ), commonly known as booklice, barklice or barkflies. The oldest known fossil lice are from the Cretaceous . Humans host two species of louse—the head louse and the body louse are subspecies of Pediculus humanus ; and the pubic louse , Pthirus pubis . The body louse has the smallest genome of any known insect; it has been used as
550-496: A parvorder, with the four subgroups listed above. These classifications are likely to change in the future as a result of ongoing phylogenetic research. 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
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#1732802121227600-422: A revised taxonomy based on a concept strongly resembling clades, although the term clade itself would not be coined until 1957 by his grandson, Julian Huxley . German biologist Emil Hans Willi Hennig (1913–1976) is considered to be the founder of cladistics . He proposed a classification system that represented repeated branchings of the family tree, as opposed to the previous systems, which put organisms on
650-422: 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, but most seem to have little effect on their host. The habit of dust bathing in domestic hens
700-429: A suffix added should be e.g. "dracohortian". A clade is by definition monophyletic , meaning that it contains one ancestor which can be an organism, a population, or a species and all its descendants. The ancestor can be known or unknown; any and all members of a clade can be extant or extinct. The science that tries to reconstruct phylogenetic trees and thus discover clades is called phylogenetics or cladistics ,
750-420: 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 ). The thoracic segments are fused, the abdominal segments are separate, and there is a single large claw at
800-576: Is a disadvantage in the context of sexual rivalry. Phthiraptera lice are members of Psocodea (formerly Psocoptera ), the order that contains booklice, barklice and barkflies. Within Psocodea, lice are within the suborder Troctomorpha , and most closely related to the family Liposcelididae . The oldest confirmed fossil louse is Archimenopon myanmarensis , an amblyceran from the Cretaceous amber from Myanmar . Another early representative of
850-420: Is also found on mammals ( lemurs ), but probably belongs to the "avian Ischnocera" and represents a host switch from birds to mammals. It is a chewing louse, which feeds on the feathers and skin debris of birds. Many of the avian Ischnocera have evolved an elongated body shape. This allows them to conceal themselves between the feather shafts and avoid being dislodged during preening or flight. The taxonomy of
900-499: Is also used with a similar meaning in other fields besides biology, such as historical linguistics ; see Cladistics § In disciplines other than biology . The term "clade" was coined in 1957 by the biologist Julian Huxley to refer to the result of cladogenesis , the evolutionary splitting of a parent species into two distinct species, a concept Huxley borrowed from Bernhard Rensch . Many commonly named groups – rodents and insects , for example – are clades because, in each case,
950-471: 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
1000-476: Is in turn included in the mammal, vertebrate and animal clades. The idea of a clade did not exist in pre- Darwinian Linnaean taxonomy , which was based by necessity only on internal or external morphological similarities between organisms. Many of the better known animal groups in Linnaeus's original Systema Naturae (mostly vertebrate groups) do represent clades. The phenomenon of convergent evolution
1050-402: Is probably an attempt by the birds to rid themselves of lice. Lice may transmit microbial diseases and helminth parasites, 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. Lice infestation
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#17328021212271100-515: Is responsible for many cases of misleading similarities in the morphology of groups that evolved from different lineages. With the increasing realization in the first half of the 19th century that species had changed and split through the ages, classification increasingly came to be seen as branches on the evolutionary tree of life . The publication of Darwin's theory of evolution in 1859 gave this view increasing weight. In 1876 Thomas Henry Huxley , an early advocate of evolutionary theory, proposed
1150-489: Is still controversial. As an example, see the full current classification of Anas platyrhynchos (the mallard duck) with 40 clades from Eukaryota down by following this Wikispecies link and clicking on "Expand". The name of a clade is conventionally a plural, where the singular refers to each member individually. A unique exception is the reptile clade Dracohors , which was made by haplology from Latin "draco" and "cohors", i.e. "the dragon cohort "; its form with
1200-557: 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. Lice have been intimately associated with human society throughout history. In the Middle Ages , they were essentially ubiquitous. At
1250-626: Is typical for mammals, and two to six for birds. Lice generally cannot survive for long if removed from their host. If their host dies, lice can opportunistically use phoresis to hitch a ride on a fly and attempt to find a new host. 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. There
1300-729: 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. 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
1350-416: 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
1400-542: The Mallophaga are paraphyletic and four suborders were then recognized: Upon finding that Phthiraptera was nested within Psocoptera , Phthiraptera, in 2021 de Moya et al. proposed reducing the rank of Phthiraptera to infraorder , and the four suborders to parvorder . These changes were accepted by Psocodea Species File and others, with the exception of placing Phthiraptera under the infraorder Nanopsocetae , as
1450-622: 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. The average number of lice per host tends to be higher in large-bodied bird species than in small ones. Lice have an aggregated distribution across bird individuals, i.e. most lice live on
1500-476: The age predicted by chimpanzee-hominid divergence . 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. 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
1550-638: The air like the real scientist Robert Boyle . 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. Despite this, the modern view is that only the body louse can transmit the disease. 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
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1600-410: The basket and the people, the world's first human beings, pour out of it in all directions. Clade In biological phylogenetics , a clade (from Ancient Greek κλάδος (kládos) 'branch'), also known as a monophyletic group or natural group , is a grouping of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on
1650-511: The character Shem the Penman infested with " foxtrotting fleas, the lieabed lice, ... bats in his belfry". 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
1700-463: 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". 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. A mediaeval treatment for lice
1750-772: The genera Austrogonoides and Nesiotinus ). The oldest known record of the group is Megamenopon rasnitsyni from the Eocene of Germany, but it is essentially a modern form, belonging to Amblycera, so the group as a whole likely has an origin in the Mesozoic. 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
1800-546: The group consists of a common ancestor with all its descendant branches. Rodents, for example, are a branch of mammals that split off after the end of the period when the clade Dinosauria stopped being the dominant terrestrial vertebrates 66 million years ago. The original population and all its descendants are a clade. The rodent clade corresponds to the order Rodentia, and insects to the class Insecta. These clades include smaller clades, such as chipmunk or ant , each of which consists of even smaller clades. The clade "rodent"
1850-596: The group is a bird louse, Megamenopon rasnitsyni , from Eckfelder Maar , Germany, which dates to the Eocene , around 44 million years ago. Saurodectes vrsanskyi from the Early Cretaceous ( Aptian ) Zaza Formation of Buryatia , Russia, has also been suggested to be a louse, but this is tentative. Placental mammal lice had a single common ancestor that lived on Afrotheria with this arising from host-switching from an ancient avian host. Cladogram showing
1900-511: The group is in need of revision, as several phylogenetic studies have found the group to be paraphyletic , specifically in regards to the two major families Philopteridae and Trichodectidae . In order to resolve this, in 2020 de Moya et al. proposed retaining the majority of the species (including Philopteridae) within Ischnocera, and then moving Trichodectidae to its own grouping called Trichodectera . Ischnocera currently consists of
1950-426: The hairs or feathers of their host and feed on skin and debris, whereas sucking lice pierce the host's skin and feed on blood and other secretions. They usually spend their whole life on a single host, cementing their eggs, called nits , to hairs or feathers. The eggs hatch into nymphs , which moult three times before becoming fully grown, a process that takes about four weeks. Genetic evidence indicates that lice are
2000-590: The last few decades, the cladistic approach has revolutionized biological classification and revealed surprising evolutionary relationships among organisms. Increasingly, taxonomists try to avoid naming taxa that are not clades; that is, taxa that are not monophyletic . Some of the relationships between organisms that the molecular biology arm of cladistics has revealed include that fungi are closer relatives to animals than they are to plants, archaea are now considered different from bacteria , and multicellular organisms may have evolved from archaea. The term "clade"
2050-518: The latter term coined by Ernst Mayr (1965), derived from "clade". The results of phylogenetic/cladistic analyses are tree-shaped diagrams called cladograms ; they, and all their branches, are phylogenetic hypotheses. Three methods of defining clades are featured in phylogenetic nomenclature : node-, stem-, and apomorphy-based (see Phylogenetic nomenclature§Phylogenetic definitions of clade names for detailed definitions). The relationship between clades can be described in several ways: The age of
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2100-463: The position of Phthiraptera within Psocodea : Philopteridae Anoplura Rhynchophthirina Trichodectidae Amblycera Liposcelididae Pachytroctidae Sphaeropsocidae Amphientometae Homilopsocidea Caeciliusetae Psocetae Epipsocetae Philotarsetae Archipsocetae Atropetae Psyllipsocetae Prionoglaridetae ( paraphyletic ) Phthiraptera is clearly
2150-400: The pubic louse ( Pthirus pubis ) fragmented into a number of minichromosomes, at least seven million years ago. Analysis of mitochondrial DNA in human body and hair lice reveals that greater genetic diversity existed in African than in non-African lice. Human lice can also shed light on human migratory patterns in prehistory. The dominating theory of anthropologists regarding human migration
2200-418: 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. The mitochondrial genome of the human species of the body louse ( Pediculus humanus humanus ), the head louse ( Pediculus humanus capitis ) and
2250-477: The size of host populations may cause a long-lasting reduction of louse taxonomic richness, for example, birds introduced into New Zealand host fewer species of lice there than in Europe. 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. The extinction of
2300-476: The skin". The human body louse Pediculus humanus humanus has (2010) the smallest insect genome known. This louse can transmit certain diseases while the human head louse ( P. h. capitis ), to which it is closely related, 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 . James Joyce 's 1939 book Finnegans Wake has
2350-601: The spread of viral infections . HIV , for example, has clades called subtypes, which vary in geographical prevalence. HIV subtype (clade) B, for example is predominant in Europe, the Americas and Japan, whereas subtype A is more common in east Africa. Ischnocera The Ischnocera is a large superfamily of lice . They are mostly parasitic on birds , but including a large family (the Trichodectidae ) parasitic on mammals . The genus Trichophilopterus
2400-668: 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. 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
2450-441: The tip of each of the six legs. 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
2500-489: Was an ointment made from pork grease, incense , lead , and aloe . 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 . 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
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