OVO-VIVIPAROUS FLIES. 117 



eggs. He was so anxious to hatch those supposed 

 eggs that he carried I hem in his pocket hy day and 

 took tlicm to bod with him at night, (as JJonuet after- 

 wards did with the eggs of aphides,) f<)r several weeks 

 successively; but instead of grubs, as he had expected, 

 perfect flies were evolved exactly similar to their pa- 

 rents. He calls them spider flics, from their resem- 

 blance to spiders; and in some parts of France the 

 species which infests horses {Hippobosca equina) is 

 called the Spaniard or J3r«ton: in England it is too 

 well known under the name of the forest fly. 



Spider flies {Hippoboscidcr, Leach.) 



We have the more willingly introduced this sub- 

 ject here, that another fly [Crativina Hiriiiulinis, 

 Oi.FERs), of the same family, has the instinct to de- 

 posit its egg-like cocoons in the warm feathery nest of 

 swallows, where they have all the necessary heat 

 which R aumur, in his experiments, was so careful to 

 maintain. In return l<)r the warmth which the voung 

 has thus received, the perlect fly, during its brief ex- 

 istence, lives by sucking the bluod of the swallows, as 

 the one first mentioned sucks the blood of horses, 

 horned cattle, and, it is also said, of man. 



