512 MOTIONS OF INSECTS. 



you come up, it flics a little further, and will thus be your avant-courier 

 for the whole length of a long field. Tliis usually fakes place, I seem to 

 have observed, when a path lies under a hedge; and perhaps the object 

 of this manoeuvre may be the capture of prey. Your motions may drive 

 a number of insects before you, and so be instrumental in supplying it with 

 a meal. Other species of the genus have the same habit. 



The aerial progress of the fly-tribes, including the gad-flies (^(Estrida), 

 horse-flies (Tabanidcc), carrion-flies (J^luscidce) , and many other genera — 

 which constitute the heavy horse amongst our two-winged fliers — is won- 

 derfully rapid, and usually in a direct line. An (Estrus about to attack a 

 horse urged to its full speed will yet keep close to it, and, at last, when 

 foiled in its object, fly away before it at a still more rapid rate.^ The 

 male Tabani, according to the observations of M. de St. Fargeau, when 

 met with in the long avenues of the continental forests, are seen to dart 

 impetuously from one end to the other, then to rest a while immovable, 

 suspended in the air, and look around on every side, and again to rush 

 with equal velocity to the other end, repeating these manoeuvres till they 

 have discovered a female, upon which they precipitate themselves, and 

 then mount together to a height which the eye cannot reach.^ An anony- 

 mous observer in Nicholson's Journal^ calculates that, in its ordinary 

 flight, the common house-fly (Musca domesiica) 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 diffe- 

 rence 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 con- 

 cerning their modes of locomotion in or upon the xoatcr. These are of 

 two kinds, swimmini:; and xvalking. 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 posterior legs 

 peculiarly fitted for it, either by a dense fringe of hairs on the shank and 

 foot, as in the water-beetles {Dytiscus), or the water-boatmen (Notonecta) . 



' Biirmcister, Manual of Enl. 463. 



• Macquarl, Diptires, i. 20. 191. ' 4to. iii. 36. 



