agility ; and clear our outlets from the annoyances of 

 gnats and other troublesome insects. Some districts 

 in the South Seas, near Guiaquil,* are desolated, it 

 seems, by the infinite swarms of venomous mosqui- 

 toes, which fill the air, and render those coasts in- 

 supportable. It would be worth inquiring whether 

 any species of hirundines is found in those regions. 

 Whoever contemplates the myriads of insects that 

 sport in the sunbeams of a summer evening in this 

 country, will soon be convinced to what a degree our 

 atmosphere would be choked with them were it not 

 for the friendly interposition of the swallows. 



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 Hippoboscce hirundines, with narrow subulated 

 wings, abounding in every nest ; and are hatched by 

 the warmth of the bird's own body during incuba- 

 tion, 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 ; and 

 to some of side-fly, from its running sideways like 

 a crab. It creeps under the tails, and about the 

 groins, of horses, which at their first coming out 

 of the north, are rendered half frantic by the tick- 



* See Ulloa's *' Travels." 



i88 



