Crab louse vs Body louse
These two are easy to mix up. Here's how to tell a crab louse from a body louse, and whether either one bites or stings.
Crab louse
Pthirus pubis
Body louse
Pediculus humanus humanus
≠The key differences
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.
Shorter, broader body and claws adapted to coarse hair; typically found in pubic hair and sometimes eyelashes, not in clothing seams.
⚖︎Side by side
| Crab louse | Body louse | |
|---|---|---|
| To humans | Itchy parasite | Disease vector |
| Size | About 1-2 mm body length | 2.3-3.6 mm long |
| Colours | Pale brown, Grey-brown, Whitish (nits) | Pale grey, Light brown, Cream |
| Family | Pthiridae | Pediculidae |
| Habitat | Coarse human body hair: pubic region most commonly; can also inhabit armpits, chest, beard, moustache, and eyelashes/eyebrows in some cases. | Human clothing and bedding; hides in seams, folds and undergarments, moves to skin to feed |
| Range | Worldwide wherever humans live; prevalence varies with sexual behavior, hygiene, and public health factors. | Worldwide wherever humans live; common historically in wartime and refugee camps, present today in areas with limited access to laundry and overcrowding |
| Active | Active year-round; most active when feeding at night or when the host is at rest. | Active year-round where conditions allow; most active when hosts wear infrequently washed clothing |
| Pest? | Yes | Yes |
🔍How to spot a crab louse
- 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.
🔍How to spot a body louse
- Look for tiny pale-grey to brown 2.3-3.6 mm insects in clothing seams, especially collars, waistbands and undergarments.
- Find eggs (nits) cemented to fabric fibers rather than to hair shafts (which indicates head lice).
- Itching and scratch marks on the torso, buttocks and thighs are common where lice feed.
- Body lice move to the skin to feed and return to clothing; inspecting clothing rather than scalp hair is key.
?Frequently asked questions
What is the difference between a crab louse and a body louse?
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. Shorter, broader body and claws adapted to coarse hair; typically found in pubic hair and sometimes eyelashes, not in clothing seams.
Is a crab louse or a body louse more dangerous?
Crab louse: Itchy parasite. Body louse: Disease vector. Crab lice bite to feed on blood and cause itching, irritation, and sometimes secondary skin infection from scratching. Bites are itchy and can cause excoriation from scratching.
Identification from photos is never certain: don't handle insects you can't identify, and get medical advice for bites, stings or allergic reactions.