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Louse-transmitted
diseases are presently not a serious threat in the United
States. In other parts of the world, however, lice do transmit
typhus fever (a disease which has killed many millions of
people), epidemic relapsing fever, and trench fever.
Lice cause much
discomfort to humans due to their bites, which are irritating,
causing sleeplessness. Scratching often leads to secondary
bacterial infections.
Head Lice
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. Eggs hatch in
five to ten days when the temperature is between 95× and
100×F. 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. Since human hair
grows about 1/2 inch per month, any nits found on a hair 1/4
of an inch from the scalp would be approximately 16-days old,
and would have hatched already, or will not hatch. These nits
are glued tightly to the hair shaft and can only be removed by
combing. A special fine-toothed comb must be used which has
teeth 0.l mm apart. A vinegar rinse is not effective.
The life cycle
for the head louse (from egg to adult) takes from 16 to 21
days.
Body Lice
Body lice spend most of their time on the
underclothing, next to the body, particularly along the seams.
From here they periodically visit the hosts’ body for blood.
They usually glue their eggs (up to 300 in a lifetime) to the
fibers of clothing, but may occasionally glue them to body
hairs as does the head louse.
Crab Lice
These lice are found mostly in the hair of the pubic
area. They may also be found under the armpits, in the beard
or mustache and on the eyebrows and eyelashes. Their
development from egg to adult normally requires from 30 to 41
days. Adult crab lice live about 30 days. Females deposit
30-50 eggs (in her lifetime). | 
Since no fossils of lice have ever been
found we can only speculate when they originated. We do know
the ancient Egyptians and Greeks wrote of them and they were
found on prehistoric American Indian mummies.