OVO-VIVIPAROUS FLIES. 



117 



eggs. He was so anxious to hatch those supposed 

 eggs that he carried them in his pocket by day and 

 took them to bed with him at night, (as Bonnet after- 

 wards did with the eggs of aphides,) for 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 flies, from their- resem- 

 blance to spiders; and in some parts of France the 

 species which infests horses {Hippobosca equina) is 

 called the Spaniard or Breton: in England it is too 

 well known under the name of the forest fly. 



Spider flies (Hippoboscidcp, Leach.) 



We have the more willingly introduced this sub- 

 ject here, that another fly {Crattrina Hirimdinis, 

 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 for the warmth which the young 

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

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

 the one first mentioned sucks the blood of horses, 

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



