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.
The female head louse will deposit from 50 to l50 eggs or nits in her lifetime. Head lice glue their eggs to the base of hairs. Only one nit is glued to any one hair. Below 74 F, most eggs will not hatch. People finding nits on hairs wonder if they are old nits which have already hatched or new nits which may still hatch.