152 NATURAL HISTORY OF SELBORNE. 



our houses ; amuse us with their migrations, songs, and marvel- 

 lous agility ; and clear our outlets from the annoyances of gnats 

 and other troublesome insects. Some districts in the South Seas, 

 near Guaiaquil,* are desolated, it seems, by the infinite swarms of 

 venomous mosquitoes, which fill the air, and render those coasts 

 insupportable. It would be worth enquiring whether any species 

 of hirundines is found in those regions. 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 were it not for the 

 friendly interposition of the swallow tribe. 



Many species of birds have their particular lice ; but the hi- 

 rundines 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 hirundinis, 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 

 feather s.f 



A species of them is familiar to horsemen in the south of Eng- 

 land 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 tickling sensation ; 

 while our own breed little regards them. 



The curious Reaumur discovered the large eggs, or rather pupce, 

 of these flies as big as the flies themselves, which he hatched in 

 his own bosom. Any person that will take the trouble to examine 

 the old nests of either species of swallows may find in them the 

 black shining cases of the pupa of these insects : but for other 

 particulars, too long for this place, we refer the reader to FHis- 

 toire d'Insectes of that admirable entomologist. Tom. iv. pi. 11. 



LETTER XVI. To THE HON. DAINES BARRINGTON. 



DEAR SIR, Selborne, Nov. 20, 1773. 



IN obedience to your injunctions I sit down to give you some 

 account of the house-martin, or martlet ; and, if my monography 



* See Ulloa's Travels. 



t The H. urfrica is, 1 think, the most annoyed by them. E0. 



