crab louse

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A parasitic louse (Phthirus pubis) that infests the pubic region and causes severe itching.

from The Century Dictionary.

• noun A kind of louse, Pediculus or Phthirius pubis or inguinalis, found at times in the hair of the pubis and perinæum, and sometimes on other portions of the body, clinging with great tenacity, and difficult to eradicate: so called from its shape and general appearance. It is destroyed by mercurial ointment.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A parasitic insect, Pthirus pubis, that lives amongst the pubic hairs of humans and feeds on blood.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a louse that infests the pubic region of the human body