Crabs cling primarily to pubic and armpit hair and feed on human blood. Itching and tiny bruises indicate the pests. They themselves hardly move and are thus quite well hidden. The vernacular often does not mince words when it comes to describing even unsavory things. Felt or pubic lice therefore have a number of colloquial pet names: Love bugs, bag rats and mast mice are just a few of them.
Features of the crab louse
However, the pet names for crabs describe some of the characteristics quite well: The crab louse (Phthirus pubis) is transmitted during close physical contact, i.e., primarily sexual intercourse, therefore feels particularly comfortable in the hair of the genital region, has six wart-like appendages similar to beetle legs, and, like the latter, belongs to the phylum of arthropods.
Of microbes and humans
Crabs are 1.5-2 mm skin parasites that like to stay where they can cling with their pincer-like claws:
- Densely hairy areas with many sweat glands, i.e. pubic, axillary, chest, abdominal and beard hair,
- In children also head hair, eyebrows and eyelashes.
They prefer to stay in one place and suck blood there in the same place sometimes for hours. The female lays 2-3 eggs (nits) per day, up to 200 in the course of their lives, and sticks them to the shaft of coarse hair. Larvae hatch from these within a week, and are fully grown after another two weeks.
During close contact with the body, however, the sluggish little animal starts to move: It can suddenly cover several centimeters to enrich its menu with the blood of a new host. The louse can survive for up to 2 days without eating in bedding, clothing and towels, and can therefore – rarely – also be transmitted through indirect contact.
Crabs occur worldwide. Exact numbers cannot be obtained. According to some studies, the risk for a crab louse infestation (pediculosis pubis) seems to depend less on socioeconomic factors such as poverty and hygiene than on the form of sexual activity (e.g., frequently changing sex partners, singleness, homosexuality).
Symptoms of a crab louse infestation
About 3-6 days after infection, symptoms appear: relatively mild, sometimes burning itching mostly in the crotch, especially at night when the bed is warm, and lentil- to fingernail-sized slate-colored to steel-blue discolorations (called taches bleues) at the bite sites. Scratching may result in additional sores.
Due to their immobility, the lice themselves or the nits can often only be seen as small dark dots or with a magnifying glass after looking for some time. Rusty brown spots can sometimes be seen in the laundry – droppings of the appetizing little animals.
Crabs: detection and therapy
The diagnosis is often made on the basis of the typical symptoms. The lice or nits can be detected microscopically if necessary. Medications are available for treatment, which are applied several times externally to the infested regions. The nits are then removed with a fine comb. If eyebrows and eyelashes are infested, removal of lice and nits using tweezers is recommended (after pre-treatment with Vaseline), as the medication is too dangerous on the eyes. Shaving or cutting the hair is not mandatory. All persons who are in close contact must be treated as well.
General measures to safely get rid of the lice are important. These include frequent changing, boiling and hot drying of towels, bed and body linen. Closing the laundry tightly in a plastic bag for three days can safely starve the parasites. An alternative is dry cleaning. Combs and brushes must be placed in hot water at about 60°C for 10 minutes and then in disinfectant for one hour.
To the point
- Crabs are bloodsuckers of humans and are found worldwide.
- Transmission occurs mainly through direct physical contact, rarely indirectly.
- Signs are itching and bluish spots.
- Family and sexual partners must also be treated.
