Crab louse

Crab louse, or pubic louse - commonly referred to as "crabs" - are a parasitic insect exclusive to humans, that feed exclusively on blood. They are typically found in pubic hair around the genitals, but can also effect other areas of the body with hair, such as eyelashes.

Crab louse can be distinguished from other species of louse by their almost-round body. Adult crab louse are typically 1-2mm long, and are smaller than the body louse and head louse. The term "crab louse" comes from their much thicker two front legs that are equipped with two large claws.



Crab louse lay eggs in the pubic hair, which then hatch after 6-8 days. They occupy three nymphal stages of development for another week to 10 days, before maturing into fully grown adults. Crab louse can live for up to 30 days.

It is estimated that crab louse effects around 2% of the population at any time, although accurate numbers are difficult to gauge as many governments do not consider crab lice infections as reportable conditions. Many people identify crab lice infections and pursue self-treatment, which also leads to a lack of reported cases.

Crab lice infections are considered a sexually transmitted infection due to the fact that crab louse only spread to a new host through close contact. As such they are primarily spread through sexual intercourse, and adults are more commonly effected than children. Infections from parent-to-child often occur through shared towels, clothing, and closets, although infections may also be indicative of potential sexual abuse. As with most other sexually transmitted pathogens, they can only survive for a short time away from a host body.

Signs and Symptoms

Infestations of crab louse are accompanied by discomfort and itching, which is caused by hypersensitivity to crab louse saliva. Infestations may also be accompanied by a signature grey-blue coloration at feeding sites, which can last for days.

Diagnosis and Treatment

Crab louse diagnosis is made using observation, where a doctor or health care specialist will examine the effected area for specific signs of crab louse.

Once identified, treatment is fairly straight forward. The most common treatments for crab lice infestations are available as over-the-counter medication containing 1% permethrin, or pyrethrins and poperonyl butoxide, which come as a moose or cream that is applied topically to the effected area. Lindane shampoo may also be prescribed if the infestation does not respond well to front-line treatment.