In the wingless insect suborder of chewing lice (Mallophaga), Trichodectes canis is the louse species that most commonly feeds on domestic dogs and other canids such as coyotes, wolves, and foxes that often have contact dogs. Unlike ticks and other parasites, the 2,800 species of biting lice described worldwide are very host specific. The dog louse or canine biting louse is about 1.5 millimeters in length with a dorsoventrally flattened body and a broad, flat head. As representatives of the Isonocera group, chewing lice extend their highly visible trisegmented antennae laterally. Each of the three pairs of legs is armed with a strong claw for digging into the host canid, even in the face of frantic biting and scratching.

View a second image of a canine biting louse.

T. canis should not be confused with the canine sucking louse, Linognathus setosus, which features a short, blunt head and seeks blood meals on dogs and their relatives. Rather than needle-like mouthparts that pierce skin, chewing lice, as their names imply, have large, opposing mandibles used to feed on hair fragments, skin, and blood. Symbiotic bacteria, found in specialized mycetocytes throughout the insect's fat reserves, are required for digestion. When the insects are deprived of their bacteria, they perish within a few days.

Having a life cycle that takes about three to four weeks, canine biting lice can be found anywhere on the dog's body. Although rarely discovered on healthy animals, poorly nourished dogs may have heavy infestations, adding to their troubles. In addition to causing severe itching and loss of sleep, Trichodectes canis can also act as the intermediate host for the dog tapeworm, Dipylidium caninum. In the case of Alaskan wolf packs infected by pets, extensive hair loss in sub-zero temperatures creates metabolic demands that reduce survival rates.

Females lay up to 100 eggs or nits. The nits of the canine biting louse are protected by an operculum and are cemented to the base of the dog's hairs. When the eggs hatch, the operculum is lost and the larva emerges through an opening. Because the entire 20-day louse life cycle is spent on the hosts, louse control primarily involves isolating and treating infested dogs with insecticides. There is no need to treat indoor carpet or backyard soils and vegetation as required with other canine pests, such as fleas and ticks. Often, adding additional Vitamin B to the dog's diet helps fight these infestations.

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