 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 scavengers , feeding on skin , fragments of feathers or hair , and debris found on the host 's body . Most are found on only specific types of animals , and , in some cases , 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 . For example , in humans , different species of louse inhabit the scalp and pubic hair . Lice generally cannot survive for long if removed from their host . Some species of chewing lice house symbiotic bacteria in <unk> in their bodies . These may assist in digestion because if the insect is deprived of them , it will die . If their host dies , lice can opportunistically use <unk> to hitch a ride on a fly and attempt to find a new host . 
