Like almost all animals lower than the mammals, the male of the body-louse is smaller and feebler than the female. The former attains a length of about 3 mm., and is about 1 mm. broad. The female is about 3·3 mm. long and about 1·4 mm. broad. It is rather bigger than the hair-louse, and its antennae are slightly longer. It so far flatters its host as to imitate the colour of the skin upon which it lives; and Andrew Murray gives a series of gradations between the black louse of the West African and Australian native, the dark and smoky louse of the Hindu, the orange of the Africander and of the Hottentot, the yellowish-brown of the Japanese and Chinese, the dark-brown of the North and South American Indians, and the paler-brown of the Esquimo, which approaches the light dirty-grey colour of the European parasites.
As plump an’ grey as onie grozet,
as Burns has it.
The latter were the forms dealt with in the recent observations undertaken by Mr. C. Warburton in the Quick Laboratory at Cambridge, at the request of the Local Government Board, the authorities of which were anxious to find out whether the flock used in making cheap bedding was instrumental in distributing vermin. Mr. Warburton at once appreciated the fact that he must know the life-history of the insect before he could successfully attack the problem put before him. At an early stage of his investigations, he found that P. vestimenti survives longer under adverse conditions than P. capitis, the head-louse.
The habitat of the body-louse is that side of the under-clothing which is in contact with the body. The louse, which sucks the blood of its host at least twice a day, is when feeding always anchored to the inside of the under-clothing of its host by the claws of one or more of its six legs. Free lice are rarely found on the skin in western Europeans; but doctors who have recently returned from Serbia report dark-brown patches, as big as half-crowns, on the skins of the wounded natives, which on touching begin to move—a clotted scab of lice! But the under-side of a stripped shirt is often alive with them.
After a great many experiments, Mr. Warburton succeeded in rearing these delicate insects, but only under certain circumscribed conditions: one of which was their anchorage in some sort of flannel or cloth, and the second was proximity to the human skin. He anchored his specimens on small pieces of cloth which he interned in small test-tubes plugged with cotton-wool, which did not let the lice out, but did let air and the emanations of the human body in. For fear of breakage the glass tube was enclosed in an outer metal tube, and the whole was kept both night and day near the body. Two meals a day were necessary to keep the lice alive. When feeding, the pieces of cloth, which the lice would never let go of, were placed on the back of the hand, hence the danger of escape was practically nil, and once given access to the skin the lice fed immediately and greedily.
His success in keeping lice alive was but the final result of many experiments, the majority of which had failed. Lice are very difficult to rear. When you want them to live they die; and when you want them to die they live, and multiply exceedingly.
Fig. 2.—Pediculus vestimenti. Dorsal and ventral views.
A single female but recently matured was placed in a test-tube, and a male admitted to her on the second day. The two paired on the sixth day and afterwards at frequent intervals. Very soon after pairing an egg was laid, and during the remaining twenty-five days of her life the female laid an average of five eggs every twenty-four hours. The male died on the seventeenth day, and a second male was then introduced, who again paired with the female. The latter, however, died on the thirtieth day, but the second male survived.