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Louse (plural: lice) is the common name for members of the
clade A clade (), also known as a monophyletic group or natural group, is a group of organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell t ...
Phthiraptera, which contains nearly 5,000 species of wingless
parasitic Parasitism is a Symbiosis, symbiotic biological interactions, relationship between species, where one organism, the parasite, lives on or inside another organism, the Host (biology), host, causing it some harm, and is adaptation (biology), ad ...

parasitic
insect Insects (from Latin ') are pancrustacean Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, Thorax (inse ...

insect
. Phthiraptera has variously been recognized as an
order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, dirt, trash, or waste, and the habit of achieving a ...
,
infraorder In biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, ...
, or a
parvorder In biological classification, the order ( la, ordo) is # a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also re ...
, as a result of developments in phylogenetic research. Lice are
obligate parasite An obligate parasite or holoparasite is a parasitic organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. ...
s, living externally on warm-blooded
hosts A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places *Host, Pennsylvania, a village in Berks County People *Jim Host (born 1937), American businessman *Michel Host (bo ...
which include every species of
bird Birds are a group of warm-blooded vertebrates constituting the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of indiv ...
and
mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which in Female#Mammalian female, females produce milk ...
, except for
monotreme Monotremes are one of the three main groups of living mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mamm ...
s,
pangolin Pangolins, sometimes known as scaly anteaters, are mammals of the order Pholidota (, from Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from aroun ...

pangolin
s, and
bat Bats are mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which in Female#Mammalian femal ...
s. Lice are
vectors Vector may refer to: Biology *Vector (epidemiology), an agent that carries and transmits an infectious pathogen into another living organism; a disease vector *Vector (molecular biology), a DNA molecule used as a vehicle to artificially carr ...
of diseases such as
typhus Typhus, also known as typhus fever, is a group of infectious diseases that include epidemic typhus, scrub typhus, and murine typhus. Common symptoms include fever, headache, and a rash. Typically these begin one to two weeks after exposure. ...
. Chewing lice live among the hairs or feathers of their host and feed on skin and debris, while 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 A nymph ( el, νύμφη, ; Ancient Ancient history is the aggregate of past eventsWordNet Search ...
, which moult three times before becoming fully grown, a process that takes about four weeks. Genetic evidence indicates that lice are a highly modified lineage of
Psocoptera Psocoptera are an Order (biology), order of insects that are commonly known as booklice, barklice or barkflies. They first appeared in the Permian period, 295–248 million years ago. They are often regarded as the most primitive of the para ...

Psocoptera
(now called
Psocodea Psocodea is a taxonomic group of insect Insects or Insecta (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area aroun ...
), commonly known as booklice, barklice or barkflies. The oldest known fossil lice are from the
Paleogene The Paleogene ( ; also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period million years ago ( Mya) to the beginning o ...
, though
molecular clock The molecular clock is a figurative term for a technique that uses the mutation rate In genetics Genetics is a branch of biology concerned with the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) Thou ...
estimates suggest that they originated earlier, during the
Cretaceous The Cretaceous ( ) is a geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of divisions ...
. Humans host two species of louse—the
head louse The head louse (''Pediculus humanus capitis'') is an obligate parasite, obligate parasitism, ectoparasite of humans. Head lice are wingless insects that spend their entire lives on the human scalp and feeding exclusively on human blood. Humans a ...

head louse
and the
body louse The body louse (''Pediculus humanus humanus'', also known as ''Pediculus humanus corporis'') is a hematophagic ectoparasite louse that infests humans. It is one of three lice which infest humans, the other two being the head louse, and the p ...
are subspecies of ''
Pediculus humanus ''Pediculus humanus'' is a species of louse Louse (plural: lice) is the common name for members of the order Phthiraptera, which contains nearly 5,000 species of wingless insect Insects or Insecta (from Latin Latin (, or , ) is a ...

Pediculus humanus
''; and the pubic louse, ''
Pthirus ''Pthirus'' is a genus of Louse, lice. There are only two extant species, and they are the sole known members of the family Pthiridae. ''Pthirus gorillae'' infests gorillas, and ''crab louse, Pthirus pubis'' afflicts humans, and is commonly known a ...
pubis''. The body louse has the smallest
genome In the fields of molecular biology Molecular biology is the branch of biology that seeks to understand the molecule, molecular basis of biological activity in and between Cell (biology), cells, including biomolecule, molecular synthesis, ...

genome
of any known insect; it has been used as a
model organism A model organism (often shortened to model) is a non-human species In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molec ...
and has been the subject of much research. Lice were ubiquitous in human society until at least the
Middle Ages In the history of Europe, the Middle Ages or medieval period lasted approximately from the 5th to the late 15th centuries, similarly to the Post-classical, Post-classical period of global history. It began with the fall of the Western Roma ...
. They appear in folktales, songs such as ''The Kilkenny Louse House'', and novels such as
James Joyce James Augustine Aloysius Joyce (2 February 1882 – 13 January 1941) was an Irish novelist, short story writer, poet, teacher, and literary critic. He contributed to the Modernism, modernist avant-garde movement and is regarded as one of the mos ...
's ''
Finnegans Wake ''Finnegans Wake'' is a book by Irish literature, Irish writer James Joyce. It has been called "a work of fiction which combines a body of fables ... with the work of analysis and deconstruction". It is significant for its experimental style and ...
''. They commonly feature in the psychiatric disorder
delusional parasitosis Delusional parasitosis (DP) is a mental disorder A mental disorder, also called a mental illness or psychiatric disorder, is a behavioral or mental pattern that causes significant distress or impairment of personal functioning. Such features ...
. A louse was one of the early subjects of
microscopy Microscopy is the technical field of using microscope A microscope (from the grc, μικρός, ''mikrós'', "small" and , ''skopeîn'', "to look" or "see") is a laboratory instrument used to examine objects that are too small to be see ...

microscopy
, appearing in
Robert Hooke Robert Hooke FRS (;  – 3 March 1703) was an English scientist, architect, and polymath, who, using a microscope, was the first to visualize a micro-organism.Howard Gest"The discovery of microorganisms by Robert Hooke and Antoni van Le ...
's 1667 book, ''
Micrographia ''Micrographia: or Some Physiological Descriptions of Minute Bodies Made by Magnifying Glasses. With Observations and Inquiries Thereupon.'' is a historically significant book by Robert Hooke Robert Hooke FRS (;  – 3 March 1703) wa ...

Micrographia
''.


Morphology and diversity

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
scavenger Scavengers are animals that consume dead organisms that have died from causes other than predation Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of ...
s, feeding on
skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have differe ...

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. If their host dies, lice can opportunistically use
phoresis hitching a ride on a fly. File:Phoresy_edited.png, A pseudoscorpion on the leg of a crane fly Phoresis or phoresy is a non-permanent, commensalistic interaction in which one organism (a phoront or phoretic) attaches itself to another (the host) ...
to hitch a ride on a fly and attempt to find a new host. Sucking lice range in length from . They have narrow heads and oval, flattened bodies. They have no ocelli, and their compound eyes are reduced in size or absent. Their
antennae Antenna (pl. antennas or antennae) may refer to: Science and engineering * Antenna (radio), also known as an aerial, a transducer designed to transmit or receive electromagnetic (e.g., TV or radio) waves * Antennae Galaxies, the name of two coll ...
are short with three to five segments, and their mouth parts, 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 (
ventral Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. Terms used generally derive from Latin or Greek language, Greek roots and used to describe something in its standard anatomical position. This ...

ventral
ly) and a food canal (
dorsally Standard anatomical terms of location deal unambiguously with the anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient ...
). 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. Chewing lice are also flattened and can be slightly larger than sucking lice, ranging in length from . 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 The Ischnocera is a large suborder of lice Louse (plural: lice) is the common name for members of the order (biology), order Phthiraptera, which contains nearly 5,000 species of wingless insect. Lice are obligate parasites, living externa ...
, but club-shaped in the suborder
Amblycera The Amblycera are a large suborder of chewing lice The Mallophaga are a suborder of louse, lice, known as chewing lice, biting lice, or bird lice, containing more than 3000 species. These lice are external parasites that feed mainly on birds, a ...
. The legs are short and robust, and terminated by one or two claws. Some species of chewing lice house
symbiotic Symbiosis (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 mil ...

symbiotic
bacteria in
bacteriocyte A bacteriocyte (Greek language, Greek for ''bacteria cell''), also known as a mycetocyte, is a specialized adipocyte found primarily in certain insect groups such as aphids, tsetse flies, German cockroaches, weevils. These cells contain Endosymbios ...
s 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 color varies from pale beige to dark gray; however, if feeding on blood, it may become considerably darker. Female lice are usually more common than males, and some species are
parthenogenetic Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and development ...
, with young developing from unfertilized eggs. A louse's
egg Diagram of a chicken egg in its 9th day. Membranes: allantois, chorion, amnion, and vitellus/ yolk. An egg is the organic vessel containing the zygote in which an embryo develops until it can survive on its own, at which point the animal ha ...

egg
is commonly called a nit. Many lice attach their eggs to their hosts' hair with specialized
saliva Saliva (commonly referred to as spit) is an extracellular fluid Extracellular fluid (ECF) denotes all body fluid outside the cells of any multicellular organism. Total body water in healthy adults is about 60% (range 45 to 75%) of total body w ...
; 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 A nymph ( el, νύμφη, ; Ancient Ancient history is the aggregate of past eventsWordNet Search ...
. 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 The head louse (''Pediculus humanus capitis'') is an obligate ectoparasite of human Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, opposable thumbs, hairlessness, and intel ...

head lice
,
body lice The body louse (''Pediculus humanus humanus'', also known as ''Pediculus humanus corporis'') is a hematophagic ectoparasite Parasitism is a symbiotic relationship between species In biology, a species is the basic unit of biologica ...
, and
pubic lice In vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, co ...
. 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 Nit comb, lice combs, and medicated shampoos or washes.


Ecology

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 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 harbor fewer taxa of lice. Bird taxa that are capable of exerting stronger antiparasitic defense—such as stronger T cell immune response or larger uropygial glands—harbor more taxa of Amblyceran lice than others. Reductions in 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 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 Chicken, domestic hens 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 is a disadvantage in the context of sexual rivalry.


Evolution

Phthiraptera lice are members of
Psocodea Psocodea is a taxonomic group of insect Insects or Insecta (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area aroun ...
(formerly
Psocoptera Psocoptera are an Order (biology), order of insects that are commonly known as booklice, barklice or barkflies. They first appeared in the Permian period, 295–248 million years ago. They are often regarded as the most primitive of the para ...

Psocoptera
), the
order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, dirt, trash, or waste, and the habit of achieving a ...
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 a bird louse, ''Megamenopon, Megamenopon rasnitsyni'' , from Eckfelder Maar, Germany, which dates to the Eocene, around 44 million years ago. ''Saurodectes, Saurodectes vrsanskyi'' from the Early Cretaceous (Aptian) Zaza Formation of Buryatia, Russia, has also been suggested to be a louse, but this is tentative. Cladogram showing the position of Phthiraptera within
Psocodea Psocodea is a taxonomic group of insect Insects or Insecta (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area aroun ...
:


Classification

Phthiraptera is clearly a Monophyly, 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 ganglion, metathoracic Ganglion, 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 Mastication, chewing lice (Mallophaga); however, subsequent classifications suggest that the Mallophaga are paraphyletic and four suborders were then recognized: * Anoplura: sucking lice, occurring on mammals exclusively * Haematomyzus, Rhynchophthirina: parasites of elephants and warthogs *
Ischnocera The Ischnocera is a large suborder of lice Louse (plural: lice) is the common name for members of the order (biology), order Phthiraptera, which contains nearly 5,000 species of wingless insect. Lice are obligate parasites, living externa ...
: mostly avian chewing lice, with one family parasitizing mammals *
Amblycera The Amblycera are a large suborder of chewing lice The Mallophaga are a suborder of louse, lice, known as chewing lice, biting lice, or bird lice, containing more than 3000 species. These lice are external parasites that feed mainly on birds, a ...
: a primitive suborder of chewing lice, widespread on birds, and also occurring on South American and Australian mammals 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 In biological classification, the order ( la, ordo) is # a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also re ...
. These changes were accepted by Psocodea Species File and others, with the exception of placing Phthiraptera under the infraorder Nanopsocetae, as a parvorder, with the four subgroups below. 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 and birds occupy. They are found even in the Antarctic, where penguins carry 15 species of lice (in the genera ''Austrogonoides'' and ''Nesiotinus''). The oldest known record of the group is ''Megamenopon, 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. 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, ''Damalinia limbata'', an ischnoceran louse from goats. The species is sexual dimorphism, sexually dimorphic, with the male smaller than the female.


Phylogeny

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–human last common ancestor, chimpanzee-hominid divergence. Because parasites rely on their hosts, hostparasite 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 a ''Pthirus'' species host-switch around 3-4 million years ago. While it is difficult to determine if a parasitehost 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 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, Pediculus humanus humanus''), the head louse (''Pediculus humanus, Pediculus humanus capitis'') and 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 Anthropology, anthropologists regarding human migration is the Recent African origin of modern humans, 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.


In human culture


In social history

Lice have been intimately associated with human society throughout history. In the
Middle Ages In the history of Europe, the Middle Ages or medieval period lasted approximately from the 5th to the late 15th centuries, similarly to the Post-classical, Post-classical period of global history. It began with the fall of the Western Roma ...
, 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". A mediaeval treatment for lice was an ointment made from pork grease, incense, lead, and aloe.
Robert Hooke Robert Hooke FRS (;  – 3 March 1703) was an English scientist, architect, and polymath, who, using a microscope, was the first to visualize a micro-organism.Howard Gest"The discovery of microorganisms by Robert Hooke and Antoni van Le ...
's 1667 book, ''Micrographia, 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 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 Typhus, also known as typhus fever, is a group of infectious diseases that include epidemic typhus, scrub typhus, and murine typhus. Common symptoms include fever, headache, and a rash. Typically these begin one to two weeks after exposure. ...
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. In the psychiatric disorder
delusional parasitosis Delusional parasitosis (DP) is a mental disorder A mental disorder, also called a mental illness or psychiatric disorder, is a behavioral or mental pattern that causes significant distress or impairment of personal functioning. Such features ...
, 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".


In science

The human body louse ''Pediculus humanus humanus'' has (2010) the smallest insect
genome In the fields of molecular biology Molecular biology is the branch of biology that seeks to understand the molecule, molecular basis of biological activity in and between Cell (biology), cells, including biomolecule, molecular synthesis, ...

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 organism A model organism (often shortened to model) is a non-human species In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molec ...
s to study the Molecular biology, molecular mechanisms behind the transmission of pathogens and Vector (epidemiology), vector Natural competence, competence.


In literature and folklore

James Joyce James Augustine Aloysius Joyce (2 February 1882 – 13 January 1941) was an Irish novelist, short story writer, poet, teacher, and literary critic. He contributed to the Modernism, modernist avant-garde movement and is regarded as one of the mos ...
's 1939 book ''
Finnegans Wake ''Finnegans Wake'' is a book by Irish literature, Irish writer James Joyce. It has been called "a work of fiction which combines a body of fables ... with the work of analysis and deconstruction". It is significant for its experimental style and ...
'' has 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 the basket and the people, the world's first human beings, pour out of it in all directions. 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. 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 William Shakespeare, 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."


See also

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


References


External links


National Pesticide Information Center – Understanding and Controlling Lice
on the University of Florida/Institute of Food and Agricultural Sciences Featured Creatures Web site
crab louse
on the University of Florida/Institute of Food and Agricultural Sciences Featured Creatures Web site
''Pediculus humanus capitis'' head louse facts, myths, life cycle at MetaPathogen

Parasitic Insects, Mites and Ticks: Genera of Medical and Veterinary Importance
Wikibooks {{Authority control Lice, Insects in culture Taxa named by Ernst Haeckel Delusional parasitosis