NATURAL HISTORY OF SELBORNE 51 



fruit in our gardens ; delight, all except one species, in 

 attaching themselves to our houses; amuse us with their 

 migrations, songs, and marvellous agility ; and clear our 

 outlets from the annoyances of gnats and other troublesome 

 insects. Some districts in the south seas, near Guiaquilf 

 are desolated, it seems, by the infinite swarms of venomous 

 mosquitoes, which fill the air, and render those coasts 

 insupportable. It would be worth inquiring whether any 

 species of hirundines is found in those regions. 2 Whoever 

 contemplates the myriads of insects that sport in the sun- 

 beams of a summer evening in this country, will soon be 

 convinced to what a degree our atmosphere would be 

 choked with them was it not for the friendly interposition 

 of the swallow-tribe. 



Many species of birds have their peculiar lice ; but 

 the hirundines alone seem to be annoyed with dipterous 

 insects, which infest every species, and are so large, in 

 proportion to themselves, that they must be extremely 

 irksome and injurious to them. These are the hippobosca 

 hirundinisy with narrow subulated wings, abounding in 

 every nest ; and are hatched by the warmth of the bird's 

 own body during incubation, and crawl about under its 

 feathers. 



A species of them is familiar to horsemen in the south 

 of England under the name of forest-fly ; 3 and to some of 



1 " See UllocCs Travels." [G. W.] 



2 There are several species of Swallows found in Ecuador, some of them being 

 resident in the country. Atlicora melano leuca is not unlike our own House- 

 Martin in appearance. [R. B. S.] 



1 The flies here mentioned constitute with some others a group no less remark- 

 able for the strangeness of their appearance than for their method of development. 

 They are all gnats, flat, with long powerful legs, which enable them to run with 

 great speed. They are mostly parasitic upon birds or mammals. The species 

 known from its abundance in the New Forest as the forest-fly (Hippobosca equina), 

 which infects horses and oxen, and a second kind, Ornithomyia avicularia, occur- 

 ring, as its name indicates, on birds of almost all kinds, possess a pair of fully deve- 

 loped wings like all typical flies ; but in another kind, Stenopteryx hirundinis^ 

 which is found on Swallows and about their nests, the wings are narrow and sickle- 

 like, and scarcely fitted for flight. Again a fourth species, the so-called deer-tick 

 (Lipoptena cervi), is provided with wings upon issuing from the pupa case, but 

 subsequently drops them after finally settling upon its host. Lastly, the so-called 



