212 FLEAS, FLUKES AND CUCKOOS 



hatching into the perfect insect. The louse-flies and the tsetse fly 

 {Glossina morsitans) y an African species, which is known to attack birds as 

 well as mammals, are viviparous. An impressive character of most 

 Diptera — as well as many other insects — is the instinctive protection 

 they afford their offspring by selecting suitable spots for laying their 

 eggs or larvae. For instance the sheep bot-fly [Oestrus ovis) deposits her 

 young larvae on the wing, striking at the eyes and nostrils of sheep or 

 goats. Sometimes she makes a mistake and darts at the eyes of shep- 

 herds whose breath smells of sheep or goat's milk. Some black-flies 

 (Simuliidae) crawl beneath running water in order to lay eggs on 

 submerged vegetation. An even more extraordinary case is that of a 

 South American warble-fly {Dermatobia hominis) which sometimes 

 attacks turkeys, causing nodule-like warbles in the superficial layers of 

 the body in which the larvae develop. This fly captures a female 

 mosquito and attaches her eggs firmly to its abdomen. When the 

 mosquito, loaded with ripe eggs, alights on some warm blooded animal 

 to feed, the larvae — apparently activated by the heat — quickly emerge 

 and penetrate beneath the host's skin. 



LOUSE-FLIES (HiPPOBOSCIDAE) 



The most highly specialised parasitic flies attacking birds are the 

 louse-flies (Plate IX). As adults they live permanently on the body of 

 the host, feed on its blood and pupate in its nest. Compared with a 

 robin a louse-fly is very large. It is over a quarter of an inch in length 

 and a small bird with one or two of these insects creeping about in its 

 feathers can be compared to a man with a couple of large shore crabs 

 scuttling about in his underclothes. 



Hippoboscids (which also attack mammals such as sheep, horses and 

 deer) display the classical specialisation for an ecto-parasitic life. Their 

 antennae are sunk in a groove and the mouth parts form a piercing 

 apparatus and a long, sheathed sucking proboscis. Their wings are 

 often reduced or absent. They are flattened dorso-ventrally with re- 

 markably tough leathery cuticles; their legs are large and muscular and 

 armed with formidable toothed claws. The whole integument is 

 covered with ugly backwardly projecting spines. They have also 

 developed an extremely efficient method of moving among feathers — 

 darting and scuttling about at a remarkable speed — and are extremely 

 difficult to catch on a living bird. This manner of progression is, in a 



