Pthirus pubis

Geographic Range

Pthirus pubis is a host specific louse found throughout the world on humans. (Burkhart and Burkhart, MAR 1999; Scott, et al., AUG 1999)


Pthirus pubis lays its eggs on coarse body hair, especially in hair associated with the pubic regions, but also in the anal region, armpits, thighs, abdomen and will even infect eyelashes and beards. These regions have flattened hairs, which the claws of P. pubis are highly modified to grasp. These lice are mostly found in unsanitary or overcrowded conditions of human hosts. (Burkhart and Burkhart, MAR 1999; Kremer and Ball, NOV 1997; Mori, et al., 1978; Roberts and Janovy, 2000; Scott, et al., AUG 1999)

Physical Description

Smaller than Pediculus humanus (head and body lice), gray "crab" lice are 1.25 to 2 mm long. Pthirus pubis has an oval body shape and is wider than it is long and these lice are given the nickname "crabs" from their shape and chelate tarsi. These lice also have small heads relative to their body size, simple eyes, and short antennae. The lice have six legs, each of which terminate with a tarsal claw. The claws on the 2nd and 3rd pairs of legs are huge compared to those on the pair of legs closest to the head, which are smaller and thinner. Pthirus pubis also has another modification of the claw region, which is actually an extension of the tibia, called the thumb of the tibia which allows it to grasp the flattened hairs of the pubic region of humans. Another distinguishing feature is the four pairs of tubercles, which stick out on each side of the animal's abdomen. Lice breathe through spiracles at the ends of these para-tergal sclerites leading to the tracheal system. (Opaneye and Jayaweera, FEB 1993; Roberts and Janovy, 2000)

  • Sexual Dimorphism
  • sexes alike
  • Range length
    1.25 to 2 mm
    0.05 to 0.08 in


All lice exhibit hemimetabolous development, consisting of three life stages: egg, nymph, and adult. The eggs of P. pubis hatch in six to eight days and the young lice then pass through three nymphal stages, lasting a total of 23 days, before becoming adults. (Roberts and Janovy, 2000)


No information is available on the mating system of these lice.

These lice reach sexual maturity about 23 days after hatching from eggs. Reproduction is sexual, with the male P. pubis inserting his aedeagus (male reproductive intromittant organ) into the female genital opening and deposting sperm. Females lay approximately 30 eggs in a lifetime and when cemented to hairs, these are called nits. (Burkhart and Burkhart, MAR 1999; Roberts and Janovy, 2000; Scott, et al., AUG 1999)

  • Breeding season
    These lice breed year-round.
  • Range gestation period
    6 to 8 days
  • Average age at sexual or reproductive maturity (female)
    23 days
  • Average age at sexual or reproductive maturity (male)
    23 days

Female lice provide nutrients to their eggs before laying them and then abandon them.

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female


These lice normally live for a little less than a month, dying soon after reproducing. However, when separated from a host, they live less than 24 hours.

  • Average lifespan
    Status: wild
    1 months


These lice are much less mobile than Pediculus humanus and can remain attached to human skin for days at a time with their claws and mouthparts engaged in the hosts' skin. When feeding, P. pubis injects saliva into the host, causing itching and pruritus. The distinctive crab-like claws of P. pubis allow it to grasp the flattened hair of the host, and they have been known to travel up to 10 cm in a day. Only found on humans, crab lice are normally transmitted directly from person to person, especially during sexual contact. Some studies have shown infants contracting these lice at birth on their scalp from an infected mother. (Kremer and Ball, NOV 1997; Opaneye and Jayaweera, FEB 1993; Scott, et al., AUG 1999; Silburt and Parsons, SEP 1990)

Communication and Perception

Presumably, lice can tell when they have hit a blood vessel when beginning to feed by sensing chemicals released at the site of the wound. Also, lice have short antennae with chemoreceptors and tactile hairs, and some, such as P. pubis, have simple eyes. No information is available on how these lice communicate with one another. (Roberts and Janovy, 2000)

Food Habits

Pubic lice feed on human blood and will die within 24 hours without having a human blood meal. Species in the order Anoplura, to which P. pubis belongs, have a highly modified feeding mechanism. They lack mandibles like all other types of lice and they have a fascicle made of four stylets which they use to feed on the blood of their hosts. The haustellum derived from the labrum supports the fascicle. Two of the stylets derived from the maxillae lock together to form a food channel. A single hollow stylet derived from the hypopharynx connects with the salivary duct and conveys salivary materials into the wound. And a large flattened stylet derived form the labium cuts into tissue with a serrated tip and serves as a guide for the other stylets. The cibarium and pharynx in the head serve as a two-chambered pump, sucking material in through the mouth and passing it on to the esophagus. (Burkhart and Burkhart, MAR 1999; Kremer and Ball, NOV 1997; Roberts and Janovy, 2000)

  • Animal Foods
  • blood

Ecosystem Roles

Pthirus pubis is an obligate ectoparasite of humans.

Species Used as Host

Economic Importance for Humans: Positive

There is often a strong correlation between the infection of Pthirus pubis in the eyelashes and individuals having other sexually transmitted diseases. Therefore, Pthirus pubis can sometimes be used as an indicator of more serious problems. (Opaneye and Jayaweera, FEB 1993; Skinner, et al., DEC 1994)

Economic Importance for Humans: Negative

Infestation of P. pubis is a sexually transmitted condition causing serious itching to its victims. Irritation is increased in the area with host scratching and the area can often become scabby with oozing lesions. Asymptomatic individuals may discover nits or lice on pubic hair, or black specks on underpants. Characteristic small blue-gray macules known as maculae caeruleae may appear at bitten sites. Complications including excoriations, secondary bacterial infections, and eczematization may ensue.

Pthirus pubis thrives in unsanitary, overcrowded living conditions and historically has been common in military, refugee, and concentration camps, prisons, and overcrowded city dwellings. Overcrowding favors P. pubis because it can migrate between hosts easily and is not always contracted through sexual contact.

Unlike body lice (Pediculus humanus), pubic lice are not known to spread typhus. (Burkhart and Burkhart, MAR 1999; Opaneye and Jayaweera, FEB 1993; Scott, et al., AUG 1999; Skinner, et al., DEC 1994)

  • Negative Impacts
  • injures humans
    • bites or stings

Other Comments

Diagnosis of an infestation is normally by a report by the victim or clinical observation of the symptoms. Doctors may perform a microscopic examination of the lice and nits for confirmation of the diagnosis.

Treatments for infestation of P. pubis include taking a shower and then applying a 1% gamma benzene hexachloride ointment or lotion. This is normally left on for 12 hours. Eyelash infestations are treated with white petrolatum ointment for 10 days. Clothing and bedding can be laundered in boiling water or dry cleaned and items inconvenient to clean should be stored away from other bedding and clothing for a month. Without blood, the lice will soon die. (Burkhart and Burkhart, MAR 1999; Mori, et al., 1978; Skinner, et al., DEC 1994)


Allison Poor (editor), University of Michigan-Ann Arbor.

Stephen Dewey (author), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor.



Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

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living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

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living in the southern part of the New World. In other words, Central and South America.

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living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

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living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


an animal that mainly eats meat


uses smells or other chemicals to communicate


having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature


union of egg and spermatozoan


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).


A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.


having the capacity to move from one place to another.

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.


found in the oriental region of the world. In other words, India and southeast Asia.

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reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.


an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death


the regions of the earth that surround the north and south poles, from the north pole to 60 degrees north and from the south pole to 60 degrees south.


an animal that mainly eats blood


reproduction that includes combining the genetic contribution of two individuals, a male and a female


living in residential areas on the outskirts of large cities or towns.


uses touch to communicate


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


Living on the ground.


the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.


living in cities and large towns, landscapes dominated by human structures and activity.


uses sight to communicate

year-round breeding

breeding takes place throughout the year


Burkhart, C., C. Burkhart. MAR 1999. Return of the silent merengue:The crab louse. Infect Med., 16 (3): 182.

Kremer, M., C. Ball. NOV 1997. Why doesn't the crab-louse (Phthirus pubis) invade the scalp?. ANN DERMATOL VENER, 124 (11): 817-818.

Mori, R., M. Hayakawa, K. Koide. 1978. 3 Cases of infection of the eyelashes by Crab Louse. FOLIA OPHTHALMOLOGY JPN, 29 (12): 1890-1892.

Opaneye, A., D. Jayaweera. FEB 1993. Pediculosis pubis- A Surrogate Marker for Sexually-Transmitted Diseases. J ROY SOC HEALTH, 113 (1): 6-7.

Roberts, L., J. Janovy. 2000. Foundations of Parasitology 2nd ed.. McGraw-Hill Higher Education.

Scott, G., K. Radcliff, I. Ahmed-Jushuf. AUG 1999. National guideline for the management of Phthirus Pubis infestation. SEX TRANSM INFECT, 75: Suppl. 1: S78-S79.

Silburt, B., W. Parsons. SEP 1990. Scalp Infestation by phthirus pubis in a six-week old infant. Pediatr Dermatology, 7 (3): 205-207.

Skinner, C., N. Viswalingam, B. Goh. DEC 1994. Phthirus pubis infestation of the eyelids: A marker for sexually transmitted diseases. INT JOURNAL STD AIDS, 6 (6): 451-452.