558 Habits of the Boat Fly. 



geese, in which there were myriads of these insects ; but, 

 during the whole term of my residence of fifteen years on the 

 spot, and passing the pond once, and often many times, in a day, 

 I never once observed the ascent of a single beetle out of the 

 water; but have, times out of number, witnessed their descent 

 in vast numbers ; and therefore conclude that they must 

 have risen in the night, or early in the morning, or come from 

 some distance to merge themselves in the pond during the 

 day. 



They descend like aerolites; but from what height, no 

 opinion can be formed. Their descent is, however, soon 

 observed and announced by the bustle of the ducks, who are 

 quickly on the alert, either with an eye turned anxiously 

 upward, or dashing to seize a beetle which has just plunged 

 into the water. The insects drop with their wings folded, 

 their own weight only, apparently, bringing them down ; and 

 though their descent through the air is most rapid, their 

 motion downwards in the water is rather slow ; because from 

 the flatted form of their bodies, and that of their oar-like feet, 

 they can only descend in spiral curves. 



It is during the devious descent that the ducks are able to 

 capture the precious morsel of their food; and the energy and 

 alacrity displayed by the flock, during a fall of the insects, is 

 really an amusing scene. Many an hour have I spent in wit- 

 nessing this sportive scramble of the ducks and ducklings in 

 this guiltless pursuit. Some fluttering along the surface, 

 others diving, and all as eager after every beetle that drops as 

 the keenest fox-hunter with the chase in view. 



That the sight of the insects is not very powerful when they 

 bemn to descend becomes evident from the circumstance of 

 their often mistaking any other reflecting surface for that 

 of water. For instance, they drop frequently on the roofs of 

 hot-houses, skylights, and glazed garden frames. Indeed, I 

 never could account for their rattling down upon the frames 

 in such numbers until I lived near the duck pond : for then 

 it was I learnt the cause of their mistaking glass for water. 



The insects fall out of the air with such force that the noise 

 of their plunge is exactly like that of a small pebble or leaden 

 bullet thrown, from a considerable height, perpendicularly, 

 into deep water; and this bubbling sound often called my 

 attention to the phenomenon, which, in the absence of ducks, 

 would have otherwise escaped notice. 



I have reason to believe that the common water shrew 

 feeds on these insects, when, in his short foraging excursions, 

 he can capture them in the mead. — James Main. Chelsea, 

 May 30. 1837. 



