Pest profile

Crab Lice (Pubic Lice)

Pthirus pubis · Psocodea: Pthiridae[2]

Crab lice are blood-feeding parasites of people, usually found in pubic hair and passed on through intimate contact.[1]

Crab louse under magnification, a small brown louse with crab-like claws gripping a hair
Crab louse under magnification, a small brown louse with crab-like claws gripping a hair. Photo: Daniel J. Drew, public domain (CC0), via Wikimedia Commons

How to identify it

  • They're grayish and about 1/16 inch, with crab-like enlarged second and third pairs of legs.[1]
  • Itching at feeding sites is often the first sign; nits may be cemented to hair shafts.[1]

Look-alikes

Look-alikeHow to tell them apart
Head liceHead lice live on the scalp and stay on the person for life.[1]
Body liceBody lice hide in clothing seams and visit the skin only to feed.[1]

Where it lives

They're one of three kinds of lice that live on people, along with head lice and body lice.[1]

Biology and life cycle

Females lay 15 to 50 white eggs at the base of coarse hairs; eggs hatch in 6 to 8 days.[1]

Development from egg to adult takes four to six weeks, and away from the body they live under 24 hours.[1]

Damage and signs

  • They sometimes move to other coarse hair such as chest, armpits or eyebrows.[1]

Health risk

Bites cause itching, and small blue dots with tenderness and swelling sometimes appear.[1]

Control

Prevention

Because they spread by close contact, an infested person should tell intimate partners.[1]

When to call a professional

Treatment is a medical matter: insecticidal lotions or shampoos from a pharmacist or physician, often repeated after 7 to 10 days.[1]

Common questions

How do you get crab lice?
Usually through intimate contact; transfer by other routes is rare because they die within a day off the body.[1]
Why repeat crab lice treatment?
A second treatment after a week to ten days kills lice that hatched after the first.[1]

Sources

  1. Clemson Cooperative Extension, Home & Garden Information Center, “Crab Lice (HGIC 2477).” hgic.clemson.edu/factsheet/crab-lice/ (accessed 2026-10-06)
  2. iNaturalist, “Pthirus pubis taxon page (order and family).” www.inaturalist.org/taxa/395978 (accessed 2026-10-06)

Updated 2026-10-14. Built from sourced records. Spot an error? Tell us.