Of insects that are not carnivorous but that live on the juices of
living flesh, such as lice and fleas and bugs, all, without exception,
generate what are called 'nits', and these nits generate nothing.

Of these insects the flea is generated out of the slightest amount
of putrefying matter; for wherever there is any dry excrement, a
flea is sure to be found. Bugs are generated from the moisture of
living animals, as it dries up outside their bodies. Lice are
generated out of the flesh of animals.

When lice are coming there is a kind of small eruption
visible, unaccompanied by any discharge of purulent matter; and, if
you prick an animal when in this condition at the spot of eruption,
the lice jump out. In some men the appearance of lice is a disease, in
cases where the body is surcharged with moisture; and, indeed, men
have been known to succumb to this louse-disease, as Alcman the poet
and the Syrian Pherecydes are said to have done. Moreover, in
certain diseases lice appear in great abundance.

There is also a species of louse called the 'wild louse', and
this is harder than the ordinary louse, and there is exceptional
difficulty in getting the skin rid of it. Boys' heads are apt to be
lousy, but men's in less degree; and women are more subject to lice
than men. But, whenever people are troubled with lousy heads, they are
less than ordinarily troubled with headache. And lice are generated in
other animals than man. For birds are infested with them; and
pheasants, unless they clean themselves in the dust, are actually
destroyed by them. All other winged animals that are furnished with
feathers are similarly infested, and all hair-coated creatures also,
with the single exception of the ass, which is infested neither with
lice nor with ticks.