Lewisi 'in a' louse (Haematopinus) is, in its main features, similar.
The following brief summary of what takes place in the plant-louse of the rose (Aphis rosae), may be regarded as typical of the family, though exceptions occur in other species.
Two species of Pediculus are found on the human body, and are known ordinarily as the head-louse (P. capitis) and the body-louse (P. vestimenti); P. capitis is found on the head, especially of children.
The name was first given in 1834 to a plant-louse which was observed to "dry up the leaves" of oaks in Provence.
The irritation is caused by the rostrum of the insect being inserted into the skin, from which the blood is rapidly pumped up. A third human louse, known as the crab-louse (Phthirius pubis) is found amongst the hairs on other parts of the body, particularly those of the pubic region, but probably never on the head.