Pubic lice, commonly called crabs, are tiny flat insects that measure 1.5 to 2.0 mm long, roughly the size of a pinhead. They earned their nickname because their squat, wide bodies and oversized claws genuinely resemble miniature crabs. You can see them with the naked eye if you look closely, though a magnifying glass makes identification much easier.
What Adult Crabs Look Like
An adult pubic louse is flat from top to bottom, giving it a low, disc-like profile when viewed from the side. It is noticeably wider and rounder than a head louse or body louse, which are longer and more narrow. The color ranges from translucent to grayish-white when unfed, shifting toward a rusty brown after a blood meal. At under 2 mm, they can look like tiny specks or flakes of skin at first glance.
The most distinctive feature is the legs. Pubic lice have six legs total, but the second and third pairs are dramatically different from the front pair. These rear legs end in large, curved claws with a thumb-like projection that wraps around a hair shaft the way your hand grips a pole. This claw structure is what anchors them firmly in place and makes them hard to simply brush off. When you spot one attached to a hair, it often appears motionless, gripping the base of the shaft close to the skin.
What Nits and Eggs Look Like
Before you see adult lice, you may notice their eggs, called nits. Nits are oval-shaped, very small, and cemented directly onto a hair shaft near the skin’s surface. They are yellowish-white to pale tan when they contain a developing embryo, and appear more translucent or whitish once the louse has hatched and left behind an empty shell.
Because nits are glued to the hair with a waterproof cement, they do not slide or flake off the way dandruff does. If you tug on what you think might be a nit and it stays firmly attached, that is a strong clue. Dandruff and skin flakes, by contrast, move freely along the hair or fall off when touched. Nits are typically found within a few millimeters of the skin, clustered in areas where the hair is coarsest.
Signs You’ll See on the Skin
The lice themselves are not the only visible evidence. Most people notice itching first, followed by small red bite marks or a rash in the affected area. Scratching can make the skin look irritated and inflamed, which sometimes gets confused with eczema or a fungal infection.
A more unusual sign is the appearance of faint blue-gray spots on the skin, called maculae ceruleae. These spots typically show up on the thighs, lower abdomen, or groin and are caused by a reaction to anticoagulant compounds in the louse’s saliva. They are painless and flat, roughly a few millimeters across, and fade on their own once the infestation is treated. Not everyone develops them, but if you notice unexplained bluish marks in combination with itching, pubic lice are a likely cause.
You may also see tiny dark specks on your underwear. These are louse droppings, which appear as rust-colored or black dots on light fabric.
How Crabs Differ From Head Lice
People sometimes wonder whether what they are seeing could be head lice that migrated, but the two look quite different. Head and body lice are longer and narrower, measuring 3 to 4 mm in adult females, nearly twice the length of a pubic louse. Their bodies have a more elongated, torpedo-like shape compared to the broad, round outline of a pubic louse. The easiest visual distinction is the width-to-length ratio: crabs are almost as wide as they are long, while head lice are clearly longer than they are wide.
Pubic lice also move more slowly than head lice and tend to stay anchored in one spot for extended periods, which is why they can be easier to find once you know where to look.
Where to Look on the Body
Pubic lice most commonly attach to coarse hair in the genital area, but that is not the only place they appear. They can also be found in armpit hair, chest hair, leg hair, facial hair (including beards and mustaches), and even eyebrows and eyelashes. They prefer coarser hair over the fine hair on your scalp, which is why head lice and pubic lice rarely swap territory.
If you suspect an infestation, check the base of the hair shafts in these areas under good lighting. A magnifying glass and a fine-toothed comb can help you spot both adult lice and nits that might otherwise blend in with the skin.
Treatment Basics
Over-the-counter treatments work well for most cases. Lotions containing 1% permethrin or mousses containing pyrethrins with piperonyl butoxide are the standard first options, available at any pharmacy without a prescription. You apply the product to the affected area, leave it on for the recommended time, then rinse. A second application about 9 to 10 days later catches any newly hatched nymphs that survived as eggs during the first round.
If crabs have reached eyebrows or eyelashes, standard insecticidal treatments should not be used near the eyes. In those cases, an ophthalmic-grade petrolatum ointment applied to the eyelid margins two to four times a day for 10 days smothers the lice and nits safely. Wash all bedding, towels, and recently worn clothing in hot water and dry on high heat to prevent reinfestation. Sexual partners from the previous month should be notified and treated at the same time.