Since no fossils of lice have ever been found we can only speculate when they originated. There are three kinds of lice which feed on man. Head and body lice are very much alike, however, body lice are slightly larger. These lice have abdomens longer than they are broad and their six legs are equal in size. In contrast, the abdomen of the crab louse is about as wide or even slightly wider than its length, and the second and third pairs of legs are thicker than the first pair.
Crab lice are much smaller than head and body lice.
There are three nymphal stages, the third followed by the adult stage. All stages must have blood meals if they are to survive and continue their development. Adult lice live about 30 days. Lice cause much discomfort to humans due to their bites, which are irritating, causing sleeplessness. Scratching often leads to secondary bacterial infections.