Conventional microscope image of the exoskeleton and some body parts of the modern human head louse, Pediculus humanus.
Credit: Vincent S. Smith, University of Glasgow

There are two main types of lice: sucking lice and chewing lice. Sucking lice have small or no eyes and feed on blood. There are over 500 different species of sucking lice. Most of these pests feed off of rodents; however, three species feed off of humans. The second category of lice is chewing lice. These lice feed on feathers, hair, blood and skin. There are over 2,500 different kinds of chewing lice and they all prefer to feed and live on animals as opposed to humans.

Head Lice are not caused by a lack of hygiene or proper sanitation. Head Lice are not able to jump or fly, and so are passed only by head-to-head contact, or by the sharing of combs, hats, and other hair accessories.

Eggs (called nits) are glued directly to the hair or feathers and nymphs feed on the parental host. Due to their need to maintain body heat, head lice cannot survive at room temperature for more than about 24 hours. Head Lice are not known to transmit infectious agents from person to person. In fact, the Harvard School of Medicine suggests that the greatest harm associated with head lice comes from the use of caustic or toxic substances in their elimination.

The ancient Egyptians would have been very sympathetic and interested in our remedies as well. They, too, were tormented by these minute parasitic creatures. Amongst the glittering treasures unearthed from ancient tombs are the remains of head lice.

Pubic Louse
Center for Disease Control

“Crab” or pubic lice lay their eggs on coarse body hair, particularly the hair associated with the pubic regions, perianal region, thighs, abdomen, and armpits; they can also infest a person's beard and eyelashes. Pubic lice are commonly called crabs because they are shorter and rounder than head and body lice, making them resemble crabs. These lice are much less mobile than head or body lice, they can remain attached with their mouth parts in the skin for days at a time.

Pubic lice are RARELY spread through sexual contact. Lice can be spread through contact with an infested person’s bed linens, towels, or clothes.
A common misunderstanding is that infestation can be spread by sitting on a toilet seat. This is NOT likely, since lice cannot live very long away from a warm human body. Lice do not have feet designed to walk or hold onto smooth surfaces such as toilet seats.

When crab lice feed they can inject saliva into the host, causing itching. Scratching the area can increase the irritation and possibly a bacterial infection. The infected area can become scaly and hardened with oozing lesions. Painless blue spots often appear after crab lice feed. Other evidence of crab lice includes rust-colored insect excretions, darker spots in underwear and flakes similar to dandruff in pubic hair.