The extinction of a bird or mammal species leads directly to the extinction of many of their parasites. Nearly 370 species of birds and mammals are listed by the IUCN as Extinct in the Wild or Critically Endangered. At least fifty species of lice share their fate, yet none appear on any list. By 1990 at least eight species of lice had already followed their host birds and mammals to extinction.
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.
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