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Pubic Lice, or Crab Lice

- Tiny, biting insects -

Summary: Pubic lice, sometimes called "crabs" or crab lice, are tiny, blood-sucking insects that cause intensely itchy lesions when they bite. They attach their eggs to the coarse hairs of the groin, armpits and sometimes eyebrows.

Jack DeAngelis, PhD
OSU Ext. Entomologist (ret.)

What are crab or pubic lice (Pthirus pubis)?

Pubic (crab) lice are tiny (1-2 mm) blood sucking insects. The common name pubic louse ("louse" is the singular form of the word "lice") comes from where they are typically found -- in the pubic area of infested individuals. They may also be found in armpit, chest and eyelash hair.

The common name crab louse describes their overall shape along with two pairs of enlarged claws, features which resemble real crabs. These modified claws are better adapted to grasp coarse hairs and this is one reason why pubic lice occur where they do. This tiny insect has been a highly specialized "companion" of humans, and our primate cousins, since before recorded history.

picture of crab, or pubic, louse

Crab, or pubic, louse soon after feeding (highly magnified). The red coloration is blood that the louse recently fed on.

Pubic lice bite to get blood. The bite leaves an intensely itchy lesion but, unlike some other blood-feeding insects, pubic lice do not transmit diseases. Scratching to relieve the intense itch can result in secondary infections, however. Pubic lice are found worldwide and are frequently spread through sexual contact.

other common name: crabs; misspelling: public lice

Crab lice eggs, or nits, on hairs

Eggs, or nits, of all human lice (head lice, body lice and crab lice) are about 1 mm long and are either glued onto individual hairs, as in head and crab lice, or laid on clothing, as in body lice. Nits need body heat in order to hatch which generally takes seven to ten days. Lice molt through several immature stages before becoming adults.

How to treat pubic lice

Pubic lice, like head lice, do not live for long off their host so treatment of the living space, and laundering of clothing, should not be your first objective. Instead, treat pubic lice with medicated lice shampoo (below).

Lice shampoo

Pubic lice should be treated like head lice infestations with medicated shampoo. One popular pubic louse shampoo contains natural pyrethrum (left). Follow package instructions carefully. Sexual partners of the infested person should be informed and possibly treated as well.

Pubic lice should not be difficult to control. Shampoos are effective when used correctly. Since pyrethrum has relatively short residual activity re-treatment 10 days after the initial treatment is required to kill lice that hatch from eggs.

Similar, blood-feeding, insect and mite pests

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Jack DeAngelis, Ph.D.

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