How large are mature lice in pediculosis and pthiriasis (lice infestation)?

Updated: Aug 16, 2019
  • Author: Lyn C C Guenther, MD, FRCPC, FAAD; Chief Editor: Michael Stuart Bronze, MD  more...
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Answer

Mature lice are 3-4 mm long (approximately the size of a sesame seed), with an elongated body, 3 pairs of legs, and narrow anterior mouthparts. Wide crab-like bodies and claws distinguish pubic lice. Nits are approximately 1 mm in length, transparent, and flask-like in appearance. (See images of lice below.)

The head louse, Pediculus humanus capitis, has an The head louse, Pediculus humanus capitis, has an elongated body and narrow anterior mouthparts. Body lice look similar but lay their eggs (nits) on clothing fibers instead of hair fibers.
The pubic louse, Pthirus pubis, is identified by i The pubic louse, Pthirus pubis, is identified by its wide crablike body.
Nit on a hair. Note the thin, translucent cement s Nit on a hair. Note the thin, translucent cement surrounding the hair shaft. Photo courtesy of David Shum, MD Western University, London Ontario.

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