Crab lice (singular, louse), scientific name Phthirus
pubis and commonly called "crabs" due to their resemblance
to the crab, are one of three kinds of human lice in the large group
of lice families, the others being head lice and body lice, which
live in clothing. They are wingless, about 1 to 3 mm long. They
attach themselves to hair strands, and hatch out of pods with lids,
or "nits", that are too tightly attached to be brushed
off but must be removed by pulling with the nails or a fine-toothed
comb.
The crab louse can live in almost any form of humanoid hair, but
is found most commonly in pubic hair, leading to its other common
name of pubic louse. Its legs are adapted to climbing along relatively
widely spaced hairs, and so can be found in eyelashes, pubic hair,
beards, moustaches, and even armpit hairs. The individual louse
can survive up to a week apart from its necessary human host, so
that crab lice can be passed on in sleeping bags and bedding. The
female may lay up to 40 eggs a time, resulting in a fluctuating
but growing population. The louse feeds on blood and can leave irritating
spots on the skin, sometimes mistaken for pimples, a condition called
Pediculosis pubis.
Pubic lice have legs that are spaced further apart than head
lice, this is an adaptation that enables them to move around more
easily in their habitat.
The female louse glues her eggs, called "nits", which
look like tiny white beads, to hair shafts. Lice bite through
the skin to suck blood, and the bite causes itching. Bites can
become secondarily infected; scratching may break the skin and
help cause secondary infection. The most common symptom of crab
lice is itching of genital area.
Pubic lice are normally spread by sexual contact and are considered
a sexually transmitted disease, but can also be spread by sharing
clothes or bedding. A common misbelief is that infestation can
be spread by sitting on a toilet seat. This is not likely since
lice cannot live long away from a warm human body. Also, lice
do not have feet designed to walk or hold onto smooth surfaces
such as toilet seats.
