MOTIONS OF INSECTS. 



291 



they precipitate themselves, and then mount together to a 

 height which the eye cannot reach. 1 An anonymous observer 

 in Nicholson's Journal* 1 calculates that, in its ordinary flight, 

 the common house-fly (Musca domestica) makes with its wings 

 about 600 strokes, which carry it five feet, every second. 

 But if alarmed, he states, their velocity can be increased six 

 or seven-fold, or to thirty or thirty-five feet in the same 

 period. In this space of time, a race-horse could clear only 

 ninety feet, which is at the rate of more than a mile in a 

 minute. Our little fly, in her swiftest flight, will in the 

 same space of time go more than the third of a mile. Now 

 compare the infinite difference of the size of the two animals 

 (ten millions of the fly would hardly counterpoise one racer), 

 and how wonderful will the velocity of this minute creature 

 appear ! Did the fly equal the race-horse in size, and retain 

 its present powers in the ratio of its magnitude, it would 

 traverse the globe with the rapidity of lightning. I would 

 here observe, however, that it seems to me, that it is not by 

 muscular strength alone that many insects are enabled to 

 keep so long upon the wing. Every one who attends to 

 them must have noticed, that the velocity and duration of 

 their flights depend much upon the heat or coolness of the 

 atmosphere, especially the appearance of the sun. The 

 warmer and more unclouded his beam, the more insects are 

 there upon the wing, and every diurnal species seems fitted 

 for longer or more frequent excursions. 



Having given you all the information that I can collect 

 with respect to the motions of perfect insects in the air, I 

 must next say something concerning their modes of locomotion 

 in or upon the water. These are of two kinds, swimming and 

 walking. Observe — I call that movement swimming, in which 

 the animal pushes itself along by strokes — while in walking, 

 the motion of the legs is not different from what it would be 

 if they were on land. Most insects that swim have their pos- 

 terior legs peculiarly fitted for it, either by a dense fringe of 

 hairs on the shank and foot, as in the water-beetles (Dgtiscus), 

 or the water-boatmen (Notonecta) ; or by having their terminal 



1 Macquart, Bipttres, i. 20. 191. 



u 2 



2 4to. iii. 36. 



