MOTIOXS OF IXSECTS. 477 



rections. The motion of its winns, if it does nof fly like a hawk, is so 

 rapid as not to be perceptible. When the crane-fly (T/pii/a oleraced) is 

 upon the wing, its fore-legs are placed horizontally, pointing forwartls, and 

 the four hind ones stretched out in an opposite direction, the one forming 

 the prow and the other the stern of the vessel, in its voyage through the 

 ocean of air. The legs of another insect of this tribe (Hirtcsa Marci) all 

 point towards the anus in flight, the long anterior pair forming an acute 

 angle with the body : — thus, perhaps, it can better cut the air. 



I have often been amused in my walks with the motions of the hornet- 

 fly {Asi/tis crnbroniformis), belonging to the second division just mentioned. 

 This insect is carnivorous, hving upon small flies. When you are taking 

 your rambles, you may often observe it alight just before you ; as soon as 

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

 the whole length of a long field. This usually takes 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 (CEsfrida;), 

 horse-flies {Tabanida:), carrion-flies {Miiscidcc), 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 CEstrus 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 awhile immoveable, 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 anonymous observer in 

 ^^icholson's Journal^ 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 



1 Burmeister, il!/an?<a/o/^n<. 463. ' 4to. ill. 36. 



2 Macquart, Dipttres, i. 20. 191. 



