INSECTS AND OTHER ORGANISMS 405 



the larvae are sheltered in the bodies of the cattle through 

 the autumn, winter, and early spring months. 



The warble-flies and other Oestridae are in the perfect 

 winged state elaborately organised Diptera, hke the blood- 

 sucking Tabanidae previously mentioned in this chapter. 

 They fly after the animals, the former to lay their eggs, the 

 latter to suck blood for food, and, their object accomplished, 

 fly away again. When, however, the insect becomes in its 

 adult stage definitely parasitic in its way of life, a tendency 

 to degeneration is usually apparent, even though the 

 adaptation to the host necessitates a degree of speciaKsation. 

 Such conditions are well exemplified by the Hippo- 

 boscidae, a small family of Diptera among whose members 

 can be observed degrees of specialised parasitism. The 

 Forest-fly, Hippohosca equina, a common insect on the 

 Continent and in parts of southern England, annoys horses 

 by alighting on their bodies, clinging to their hairs and suck- 

 ing their blood. Its feet carry strong-toothed claws as well 

 as highly developed adhesive pads and complex feathery 

 hairs, so that it secures firm hold of the coat of the horse 

 on which it settles ; more than a hundred of these flies have 

 been observed crawling or clinging on a horse's back or 

 limbs, and it has been stated by E. A. Ormerod (1896) and 

 others that the animal suffers more irritation from the 

 insects' incessant movements over its body than from their 

 blood-sucking activities. The forest-fly's wdngs are of 

 normal length for its size but relatively narrow. In the 

 allied Ornithomyia avicularia which attacks various birds 

 the wings are still narrower, and in Lipoptera hirundinis, a 

 well-known parasite of swallows, often found in their nests, 

 these organs are reduced to short strap-like vestiges. The 

 well-known " Ked " of sheep {Melophagus ovinus) with feet 

 elaborately specialised for clinging, like those of Hippobosca, 

 is altogether wingless. Various members of this family 

 illustrate, therefore, the establishment of winglessness as an 

 accompaniment of parasitism. It is of interest to notice 

 among them a remarkable specialisation of life-history. 

 Instead of laying an egg or giving birth to an early-stage 



