Chewing and Sucking Lice: Phthiraptera

Most louse species remain attached to their host for their entire lives. Their populations vary greatly in size and are strongly influenced by the condition and health of their hosts. For example, birds with damaged bills or feet may have more lice because they are unable to preen or clean themselves efficiently. Some lice escape preening by wedging themselves between feather barbs or by living at the bases of fluffy feathers on the bird's abdomen. They will bite into the feathers with their mouthparts and lock their jaws in place. Some species go to the extreme of actually living inside the quills of wing feathers to escape preening by their shorebird hosts. The dead, dried bodies of lice are found firmly attached to bird and mammal skins in museum collections, sometime hundreds of years after the collection and death of their host.

Direct physical contact between hosts is usually the best way for lice to disperse within a host species population. Host animals also pick up new lice by sharing nests and nest materials with other infested animals. One of the most unusual and rare methods of louse dispersal is by means of phoresy (FOR-uh-see), or hitchhiking. These lice attach themselves to the abdomens of certain flies and hitch a ride to the next host.

For most species of lice, it is known that there are both males and females and they reproduce primarily by mating. A few species reproduce by parthenogenesis (PAR-thuh-no-JEH-nuh-sihs), a process where the young develop from unfertilized eggs. Females glue their whitish eggs, also known as nits, to parts of feathers or hair shafts. Human body lice will sometimes attach eggs to clothing fibers that stick from the garment like hairs. Eggs usually take four to ten days to hatch depending on species and temperature. The larvae (LAR-vee), or young of an animal that must change form before becoming adults, closely resemble the adults but are incapable of reproducing. They develop gradually through a series of molts, shedding their exoskeletons or hard outer coverings four times before reaching adulthood. Adult lice live for about a month. Human body lice will lay 50 to 150 eggs in their lifetime.