Question:
What are called "crabs" are one varient of lice, similar to head and body
lice, but adapted to living in the pubic region and being sexually
transmitted. Lice are sometimes called "cooties." The pubic variety are more
crablike with shorter bodies and have a bigger and nastier set of middle and
hind claws for gripping pubic hair, but otherwise are just lice (six-legged
insects). "Nits" are simply the egg cases of lice, attached to individual
hairs with stickem and showing up as a little inert thing stuck to the hair,
like a preying mantis egg case. These don't move and are clearly not the
critter. All species of lice (head, body, pubic) make these nits. They are
combed out of hair with fine lice combs, or else by "nitpicking" (a word
which has lost its origin in this age of sanitation). Only body lice
transmit diseases like typhus. Head lice are more of a social stigma than a
real public health problem, dispite your local elementary school's probable
hysteria.
Lice are all easily visible to the naked eye, but not so the tiny mite which
causes scabies. These are no more than a moving black dot under the best of
seeing conditions, and as they are often buried, you can't alway see that.
Mites are crustacea like lice, but otherwise are ten-legged beasties, more
closely related to spiders than to lice (which, as has been noted, are
insects, like fleas). Scabies show up as itchy red bumps that are more like
a series of mosquito bites, and these have the same origin because they are
an allergic reaction, in this case to to mite feces rather than to mosquito
saliva. Mites/scabies can be transmitted sexually or non-sexually. They
are harder to get rid of (lots of smelly lotion), and it takes longer.
Sometimes the diagnosis is delayed, especially with minor infections and
non-savvy doctors.
Hope this all helps.
Answer:
Therefore, in a life filled with pain and tragedy, it is vitally
important I give you the _scientifically accurate_ distinction between
"insects" and "crabs":
Insects, as you note, have six legs. Apperently, six, being the
smallest even number above four, was felt to be the smallest number of
legs a self-respecting arthropod could wield so as to avoid confusion
with a vertebrate. And very popular this arrangement was.
Crabs, however, in all their scientific, folkloric and taxonomic
senses, big and little, have _too many_ legs, or to be perfectly
correct, too many damn appendages.
This can be verified by visiting an King Crab at your local aquarium:
I dare you to try to count and classify his appendages; they are
altogether horrible in number, and may be fractal! Eating is the only
thing which will tame his podophillic tendencies.
