# Crab louse (Pthirus pubis) > A small, crab-shaped parasitic louse that lives on human coarse hair (especially pubic hair) and feeds on blood. Source: https://insectscanner.com/species/crab-louse/ (updated 2026-10-10) ## Is it dangerous? **Itchy parasite.** Crab lice bite to feed on blood and cause itching, irritation, and sometimes secondary skin infection from scratching. They are not known to transmit systemic diseases. First aid: avoid scratching, clean the area, and seek treatment with recommended topical therapies; consult a healthcare provider for diagnosis and treatment options and for infestations of eyelashes. **Pets:** Does not infest dogs, cats, or other pets; species is specific to humans. ## Quick facts - Scientific name: Pthirus pubis - Also called: Pubic louse, Crabs - Order: Phthiraptera (Lice) - Family: Pthiridae (Pubic lice) - Size: About 1-2 mm body length - Colours: Pale brown, Grey-brown, Whitish (nits) - Habitat: Coarse human body hair: pubic region most commonly; can also inhabit armpits, chest, beard, moustache, and eyelashes/eyebrows in some cases. - Range: Worldwide wherever humans live; prevalence varies with sexual behavior, hygiene, and public health factors. - Active: Active year-round; most active when feeding at night or when the host is at rest. - Lifespan: Adults live up to about a month on a human host; off the body they die within 1-2 days. - Effect on plants: Harmless - Pest: yes ## Overview Pthirus pubis (the crab louse) is a tiny, obligate parasite of humans that lives in coarse body hair and feeds on blood. It spreads mainly by close personal contact, especially sexual contact, but can occasionally be transferred via bedding or clothing. Infestations cause itching and visible eggs (nits) glued to hairs; they are not known to transmit other infectious diseases. Infestations are treatable with topical insecticidal preparations and mechanical removal of lice and nits, combined with cleaning of clothing and bedding. ## How to identify it Adults are stout, crab-like insects about 1-2 mm long with a broad, rounded body. They have six legs: the front pair is slender, while the middle and hind legs are thick and end in large claws adapted for grasping coarse hairs. Nits (eggs) are small, opalescent to yellowish-white ovals firmly cemented to the base of individual hairs. Nymphs resemble small, translucent adults and become more pigmented after feeding. - Look for tiny crab-shaped insects about 1-2 mm long clinging to coarse hairs, especially in the pubic area. - Find oval nits glued firmly to hair shafts close to the skin; nits do not wipe off easily. - Intense itching in the pubic region, visible crawling insects, or blue-gray skin spots from bites (maculae caeruleae) can indicate infestation. ## Lookalikes - **Head louse** (Pediculus humanus capitis): Head lice are more elongated, slightly larger, and inhabit scalp hair rather than coarse body hair; claws are adapted to thinner hairs. - **Body louse** (Pediculus humanus humanus): Body lice live in clothing and move to skin to feed; they are associated with poor hygiene and crowded conditions and differ in body shape from the crab louse. ## Life cycle - **Egg (nit):** Eggs are cemented to individual hairs near the skin; they hatch in about 6-10 days depending on temperature. - **Nymph:** Nymphs look like small translucent adults and go through three molts over about 2-3 weeks before becoming sexually mature adults. - **Adult:** Adults are about 1-2 mm, feed on blood several times a day, mate on the host, and females lay eggs glued to hairs. ## Diet and predators - Young eat: Blood from the human host - Adults eat: Blood from the human host - Predators of the young: Occasionally killed by grooming or by removing hairs; specific predators not relevant in the human-hair microhabitat - Predators of adults: Removed by host grooming, washing, or insecticidal treatment; natural predators are not a control factor ## Effect on plants and gardens Not relevant; this species feeds only on humans. ### How to get rid of it Treat with an over-the-counter lice treatment containing permethrin 1% or pyrethrins with piperonyl butoxide, following the label, and repeat if advised; ask a healthcare provider if it fails, and never use these products near the eyes (eyelash infestations need medical care). Remove nits with a fine comb or fingernails. Machine-wash bedding, towels and clothing used in the previous 2-3 days in hot water and dry on high heat, or seal them in a bag for 2 weeks. Sexual partners should be treated at the same time, and avoid close contact until treatment is complete. ## Where and when to find it Inspect coarse human hairs: pubic region first, then armpits, chest, beard/moustache, and eyelashes/eyebrows. Look for crawling lice or nits attached near the base of hairs. - Best time: Any time of year; easier to spot when symptoms (itching or visible movement) occur. Nighttime may be when lice feed and are more active. - Tips: Use a magnifying glass and bright light, part the hair close to the skin, and check for nits close to hair roots. Seek medical advice rather than attempting strong insecticides on sensitive areas. ## Fun facts - Crab lice have a broad, crab-like body; their large, crab-like claws are on the middle and hind legs and are specialized for gripping coarse hairs. - They cannot survive long off a human host—usually less than 24-48 hours—because they require regular blood meals. ## Frequently asked questions ### Do crab lice bite? Yes. They pierce the skin to feed on blood, which causes itching and sometimes small blue-gray spots from healed bites. ### Are crab lice dangerous? Not generally. They cause itching and discomfort and can lead to secondary skin infection from scratching, but they are not known to transmit other serious diseases. ### How do I get rid of crab lice? Use approved topical treatments (for example pyrethrin with piperonyl butoxide or permethrin 1% cream rinse) following product instructions or a healthcare provider's advice, remove nits by combing or plucking, wash bedding and clothing in hot water (at least 60 degrees C) and dry on high heat, and avoid sexual contact until treatment is complete. Eyelash infestations require special medical care. ### Can I get crab lice from toilet seats or swimming pools? Transmission from inanimate objects is unlikely because lice need close contact and do not survive long off the body. The most common route is direct person-to-person contact, especially sexual contact. ### Can pets spread pubic lice? No. Crab lice are specific to humans and do not infest pets. --- More about this species: [iNaturalist](https://www.inaturalist.org/taxa/395978), [Wikipedia](https://en.wikipedia.org/wiki/Crab_louse). Identify insects and spiders from a photo with the Insect Scanner iPhone app: https://apps.apple.com/app/id1543946563?pt=126685406&ct=web-markdown&mt=8 Identification from photos is never certain: don't handle insects you can't identify, and get medical advice for bites, stings or allergic reactions.