Lice (singular: louse), (order Phthiraptera), are an order of over 3,000 species of wingless insects; three of which are classified as human disease agents. They are obligate ectoparasites of every avian and most mammalian orders. They are not found on Monotremes (the platypus and the echidnas or spiny anteaters) and a few eutherian orders, namely the bats (Chiroptera), whales, dolphins and porpoises (Cetacea) and pangolins (Pholidota).
Lice feed on skin (epidermal), sebaceous secretions and blood. A louse's color varies from pale beige to dark grey; however, if feeding on blood, it may become considerably darker. They mostly like clean hair.
A louse's egg is commonly called a nit. Lice attach their eggs to their host's hair with specialized saliva which results in a bond that is very difficult to separate without specialized products. Living lice eggs tend to be pale white. Dead lice eggs are more yellow. Lice are very annoying and are difficult to remove, but not impossible. Lice infestations can be controlled with lice combs, and medicated shampoos or washes.
It has been suggested that the order is contained by the Troctomorpha suborder of Psocoptera. Lice can not jump or fly.
Recent DNA evidence suggests that pubic lice spread to the ancestors of humans approximately 3.3 million years ago from the ancestors of gorillas by sharing the same bed or other communal areas with them, and are more closely related to lice endemic to gorillas than to other lice species infesting humans.