A louse is a group of small, wingless insects. Parasites are divided into two main groups: chewing or biting lice, which are parasites of birds and mammals, and sucking lice, parasites of mammals only. One of the sucking lice, the human louse, lives in filthy and overcrowded conditions and is a carrier of typhus and relapsing fever.

Origin of the species and description

Photo: Louse

Photo: Louse

It is generally accepted that lice are descended from book lice (order Psocoptera). It is also accepted that chewing lice are related to sucking lice, some researchers believe that they evolved from offspring before division into species, others that they differed from species already parasitic on mammals. The origin of elephant lice is unclear.

Other than a louse egg found in Baltic amber, there are no fossils that could provide information about the evolution of lice. However, their distribution is somewhat similar to the history of fossils.

The genus of chewing lice often has a number of species that are limited to a single bird species or group of closely related birds, suggesting that the genus assigned to the order of birds was parasitized by an ancestral stock of chewing lice that diverged and evolved along with the divergence and evolution of its bird hosts. .

Video: Louse

This host-parasite relationship may shed some light on host-parasite relationships. Commonly placed with storks, flamingos are parasitized by three genera of sucking lice found elsewhere only in ducks, geese and swans and may therefore be more closely related to these birds than to storks. The louse closest to the lice of the human body, — it's a chimpanzee louse, and a human's — gorilla pubic louse.

However, a number of factors obscured the direct relationship between louse species and host species. The most important of these is secondary infestation, which is the appearance of louse species on a new and unrelated host. This could have happened at any stage in the evolution of the host or parasite, so that subsequent divergence obscured all traces of the original host change.

The length of the flattened bodies of lice is from 0.33 to 11 mm, they are whitish, yellow, brown or black. Probably all bird species have chewing lice, and most mammals have chewing or sucking lice, or both.

Appearance and Features

Photo: What a louse looks like

Photo: What a louse looks like

The louse's body is flattened dorsoventrally with a long, horizontal head axis, allowing it to lie close along feathers or hair for attachment or feeding. The shape of the head and body varies considerably, especially in chewing bird lice, in adaptation to different ecological niches on the host's body. Birds with white plumage, such as swans, have a white louse, while a cat with dark plumage has an almost completely black louse.

The antennae of the louse are short, three to five segments, sometimes they are modified in the male as constricting organs to hold the female during mating. The mouths are adapted for biting in biting lice and highly modified for sucking in suckers. Sucking lice have three needles, which are located in a sheath inside the head, and a small trunk armed with recursive tooth-like processes, probably to hold the skin during feeding.

Elephant lice have chewing mouthparts, with modified mouths that end with a long proboscis. The thorax may have three visible segments, may have a fusion of mesothorax and metathorax, or all three may be fused into one segment, as in sucking lice. The paws are well developed and consist of one or two segments. The birds inhabited by the chewing louse have two claws, and some of the mammal-infested families have one claw. Sucking lice have one claw opposite the tibial process, which forms an organ that compresses the hair.

The belly of a louse has eight to 10 visible segments. There is one pair of thoracic respiratory pores (spiracles) and a maximum of six abdominal pairs. The unstable male genitalia provide important features for species classification. The female does not have a distinct ovipositor, but the various lobes present on the last two segments of some species may serve as egg guides during laying.

The alimentary canal consists of the esophagus, a well-developed midgut, a smaller hindgut, four Malpighian tubules, and a rectum with six papillae. In sucking lice, the esophagus passes directly into the large midgut, with or without swelling. There is also a strong pump connected to the esophagus to draw in blood.

Where does the louse live?

Photo: Insect louse

Photo: Insect louse

Many birds and mammals are infested with more than one type of lice. Often they have at least four or five kinds of lice. Each species has specific adaptations that allow it to inhabit specific areas of the host's body. Among bird chewing lice, some species occupy different areas of the body for resting, feeding, and laying eggs.

Fun Fact: The louse cannot live for shorter periods of time away from its owner, and the adaptations serve to keep it in close contact. The louse is attracted by body heat and repelled by light, which causes it to remain in the warmth and darkness of the host's plumage or husk. It is also likely to be sensitive to the scent of its owner and the characteristics of its feathers and hairs that help it navigate.

A louse may leave its host temporarily to move on to another host of the same species, or to a host of a different species, such as from prey to predator. Chewing lice are often attached to flying lice (Hippoboscidae), which also parasitize birds and mammals, as well as other insects, by which they can be transferred to a new host.

However, they may not be able to settle on a new host due to chemical or physical incompatibility with the host in matters of food or habitat. For example, some mammalian lice can only lay their eggs on hairs of a suitable diameter.

Lack of frequency of transmission from one host species to another results in host specificity, or host restriction, in which a particular louse species is found in only one host species or a group of closely related host species. It is likely that some host-specific species evolved as a result of isolation because there was simply no way for lice to be transmitted.

Pet and zoo animals sometimes have multi-host lice populations, and pheasants and partridges often have thriving chicken lice populations. Heterodoxus spiniger, which parasitizes domestic dogs in tropical regions, most likely was acquired relatively recently from an Australian marsupial.

Now you know where the louse is found. Let's see what this insect eats.

What does a louse eat?

Photo: Lice

Photo: Lice

Sucking lice feed exclusively on blood and have mouth organs well adapted for this purpose. Fine needles are used to puncture the skin, where salivary secretions are injected to prevent coagulation as blood is sucked into the mouth. The needles are retracted into the head when the louse is not eating.

Chewing bird lice feed on:

  • feathers;
  • blood;
  • tissue fluids.

They obtain liquids by chewing on the skin, or, like bird lice, from the central pulp of the developing feather. Chewing lice that feed on feathers are able to digest the keratin from the feathers. It is likely that mammalian chewing lice do not feed on hair or hair, but on the remains of the skin, secretions, and possibly sometimes blood and tissue fluids.

Lice infestation develops mainly during the cold season and peaks in late winter and early spring. Skin temperature is also related to the severity of the lice infestation. The number of lice decreases in the hot season. A poor winter diet weakens the cattle's natural defenses against lice infestation. A denser and wetter coat in winter creates excellent conditions for the development of lice.

In the spring, food is found quickly when the herds begin to graze on new pastures. Shorter coats and sun exposure reduce skin moisture, and free-range grazing ends with overcrowding in winter quarters, which also reduces transmission. As a consequence, lice infestations usually spontaneously decrease during the summer season. However, a few lice usually manage to survive some of the animals, which re-infest the whole herd when they return to winter the following winter.

Characteristics and lifestyle

Photo: White louse

Photo: White louse

Lice spend their whole lives on the same hosts: transmission from one host to another is carried out through contact. Transmission from herd to herd usually occurs by introducing an infected animal, but flies can also occasionally carry lice.

Up to 1-2% of cattle in a herd can carry large numbers of lice even in summer when high temperatures reduce lice numbers. These carrier animals are a source of reinfection during cold snaps. Usually it is a bull or a cow in poor condition. Winter shelter provides ideal conditions for the transfer of lice between livestock.

Fun fact: Outbreaks of disease caused by lice were common by-products of famine, war, and other disasters before the advent of insecticides. Due in part to the widespread use of insecticidal shampoos for control, the head louse is resistant to many insecticides and is reemerging in many regions of the world.

A severe lice infestation can cause severe skin irritation, and damage to the outer skin can lead to secondary infections. Domestic animals may also experience chafing and damage to hides and wool, and meat and egg production may be reduced. In heavily infested birds, the feathers can be very damaged. One of the dog lice is an intermediate host of a tapeworm, and a rat louse is a transmitter of mouse typhus among rats.

Social structure and reproduction

Photo: Black Louse

Photo: Black louse

With the exception of human body lice, lice spend their entire life cycle, from egg to adult, on the host. Females are usually larger than males and often outnumber them on a single host. In some species, males are rare, and reproduction occurs by unfertilized eggs (parthenogenesis).

The eggs are laid singly or in clumps, usually attached to a feather or hair. The human louse lays its eggs on clothing near the skin. Eggs may be simple ovoid structures, glistening white among feathers or hairs, or may be heavily sculpted or decorated with protrusions that help attach the egg or serve for gas exchange.

When the larva inside the egg is ready to hatch, it sucks air through the mouth. Air passes through the alimentary canal and accumulates behind the larva until sufficient pressure is created to push back the lid of the egg (callus).

In many species, the larvae also have a sharp lamellar structure, an incubation organ in the head region, which is used to open the gill bone. The emerging larva is similar to the adult, but is smaller and uncolored, has fewer hairs, and differs in some other morphological details.

Metamorphoses in lice are simple, in larvae molting occurs three times, each of the three stages between molts (ages) becomes larger and more like an adult. The duration of the various developmental stages varies from species to species and within each species depending on temperature. In the human louse, the egg stage can last from 6 to 14 days, and the stages from hatching to adult — 8 to 16 days.

Fun fact: The life cycle of a louse can be closely related to the specific habits of the host. For example, the elephant seal louse must complete its life cycle within the three to five weeks, twice a year, that the elephant seal spends ashore.

Photo: What a louse looks like

The enemies of lice are the people who fight them. Classic dipping and spraying concentrates with traditional contact insecticides (mainly organophosphorus compounds, synthetic pyrethroids and amidines) are quite effective lacicides for cattle. However, such insecticides do not kill lice eggs (nits) and their residual effect is usually not sufficient to ensure that immature lice are killed when the eggs are hatched.

A variety of compounds are effective in controlling lice in cattle, including the following:

  • synergized pyrethrins;
  • synthetic pyrethroids;
  • cyfluthrin;
  • permethrin;
  • zeta-cypermethrin;
  • cyhalothrin (including gamma- and lambda-cyhalothrin, but only for cattle).

Many pyrethroids are lyophilic, which facilitates the development of well-spreading irrigation formulations. Natural pyrethrins are rapidly degraded, while synthetic pyrethroids such as flumethrin and deltamethrin are more stable and have a relatively long duration of action, but they do not affect all developmental stages of the lice life cycle.

Organophosphorus compounds such as phosmet, chlorpyrifos (for beef and non-lactating dairy cattle only), tetrachlorvinphos, coumaphos and diazinon (for beef and non-lactating dairy cattle only) are also used against lice.

Compounds such as macrocyclic lactones, ivermectin, eprinomectin and doramectin are used to control lice in cattle. Injectable macrocyclic lactones also control lice bites as they reach the parasites through the host's bloodstream. But control of chewing lice is usually incomplete. Medicinal formulations are effective against lice bites, while injectable formulations are primarily effective against biting lice.

Population and species status

Photo: Louse

Photo: Louse

There are about 2,900 known species of chewing or biting lice, many more not yet described, and about 500 sucking species. Lice have not been found on platypus or on anteaters and armadillos, and are not known to exist on bats or whales. Lice population density varies greatly between individuals and also depends on the season.

Sick animals and birds with damaged beaks, probably due to lack and cleaning, may have an unusually high number: more than 14,000 recorded lice on a sick fox and more than 7,000 on a cormorant with a damaged beak.

The number of lice found on healthy hosts is usually significantly lower. In addition to host care and maintenance, lice and their eggs can be controlled with predatory mites, dust baths, intense sunlight, and constant moisture.

Lice infestations are more common in young, old, or debilitated animals, or animals that kept in unsanitary conditions. Chewing lice are quite common on dogs and cats around the world. Another chewing louse, Heterodoxus spiniger, is found on dogs in tropical areas such as the Philippines. Sucking louse infestations are most common in colder climates, to which this louse is mostly restricted.

Louse — it is a parasite that is distributed throughout the world. These species are host-specific and are divided into biting and sucking lice. Differentiation of head morphology, host species, and sometimes location on the host is usually sufficient to identify lice for diagnostic purposes. Lice infestation is called pediculosis.

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