Order Siphunculata (= Anoplura) - Sucking Lice

• Human Louse (Hair & Body Louse)
• Human Crab Louse
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Small, wingless insects living as external parasites of mammals. Head usully narrow and the eyes are reduced or absent. Antennae short. Mouthparts highly modified for piercing and blood-sucking, and retracted into the head when not in use. Body usually flattened, with all the thoracic segments fused together. Cerci absent. The legs have one tarsal segment ending in a strong claw. The claw is hinged in such a way that it can be closed tight against the tarsus to grip the hair of its host. There are three nymphal stages, with no obvious metamorphosis. About 500 species are known, with less than 50 of these recorded in the British Isles.

Sucking Lice feed exclusively on blood, obtained by piercing the skin of their host. As with the Biting Lice, most are confined to one host or a group of closely related host species. The best known family is the Pediculidae, on account of its human-infesting species (see below). The most important of the other Sucking Lice are those of the family Haematopinidae, which affect domestic livestock such as pigs, sheep and cattle.

Description. The Human Louse exists as two distinct races - the Head Louse (P. humanus capitis) and the Body Louse (P. humanus corporis). The Head Louse is more or less whitish in colour and up to 3 mm long; the Body Louse is generally darker and larger, up to 5 mm long.

Biology. Found on the hairy parts of the human body. The Head Louse is more or less confined to the hair of the head and children seem to be more susceptible than adults. Heavy infestations frequently occur among school children, but this does not imply any lack of attention to hygiene, for the lice and their eggs can withstand vigorous washing and combing. Fortunately, the Head Louse does not appear to carry any diseases. The Body Louse lives chiefly on the front and back of the torso. It is generally less common than the Head Louse, except in circumstances of poor hygiene due to infrequent washing and changing of clothes. The bite of the Body Louse can be very irritating and it is known to transmit several diseases, including typhus, relapsing fever and trench fever. Both forms usually cement their white eggs (commonly known as 'nits') to the hair, although eggs are sometimes also attached to clothing or even scattered loosely. Development is fairly rapid and can be as short as 15-20 days from the egg to adult stage.

Distribution. Cosmopolitan.

Photo: V.J. Stanek ©

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Adult Body Louse

Egg (or 'nit') attached to hair

Description. Short, broad body with rather stout claws on the middle and hind legs. Greyish-white to reddish in colour. Up to 2 mm long.

Biology. Lives on the hairy parts of the human body, but confined to the pubic areas and other lower parts. The life cycle is similar to that of the Human Louse. It is not known to carry any diseases.

Distribution. Cosmopolitan.

Photo: V.J. Stanek ©