SOME WINGLESS INSECTS 163 



and wooden beds, while grubs of cat and dog fleas may be found 

 among the bedding material provided for those domestic pets. 

 It has been stated that in many cases the grub must have as 

 part of its food " half-digested blood passed through the 

 parent flea's body "- 1 The length of the larval period varies 

 in different kinds of fleas, and under different conditions of 

 climate, from less than a week to four months. 



When fully grown, the flea-grub spins a cocoon (Fig. 92 j) 

 by fastening together, with silky secretion, fragments of its 

 dwelling place ; such a cocoon is round or oval in shape, and 

 naturally inconspicuous on account of its composition. Within 

 this cocoon the last larval cuticle is cast and the pupa (Fig. 

 92 k) revealed ; the pupal stage, even in the same species, may 

 vary in duration from less than a week to more than a year. 

 In the pupa the characteristic features of the adult are clearly 

 recognizable, having been formed, as in metamorphic insects 

 generally, from imaginal buds. The life-history of a flea 

 affords, therefore, the interesting condition that it resembles 

 closely that of an insect which undergoes the hidden type of 

 wing-growth, although no wings are ever developed. 



The larvae of fleas resemble in general aspect those of certain 

 midges and other insects belonging to the order of the two- 

 winged flies (Diptera) with which the fleas may have some 

 affinity. In any case it is of interest to trace how, among 

 certain members of the Diptera the parasitic habit is accom- 

 panied by a reduction in size or total disappearance of the 

 wings. Many Diptera of various families such as breeze- 

 flies, gnats, the stable-fly (Stomoxys) and the African Tsetse 

 (Glossina) habitually suck blood from large animals ; these all 

 fly actively, resting perhaps, for a short time on the body of 

 the victim and then darting away again. But the Forest-fly 

 (Hippobosca), which often attacks horses in the south of 

 England, is provided with strong clinging claws as well as with 

 adhesive pads and plumose hairs, which enable it to hold on 

 to the hairs of the animal whose blood it draws. It happens, 

 therefore, that these insects often spend a long time on the 

 bodies of their hosts, scores or more than a hundred of them 

 being sometimes found crawling over the body of a single 



1 J. Waterston : " Fleas as a Menace to Man and Domestic Animals ". 

 Brit. Mus. (Nat. Hist.) Econ. Series No. 3. London, 1916. 



