MOTIONS OF INSECTS. 417 
rections. The motion of its wings, if it does not fly like a hawk, is so 
rapid as not to be perceptible. When the crane-fly (Zipula oleracea) is 
upon the wing, its fore-legs are placed horizontally, pointing forwards, 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 (Hirtea Marci) alk 
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 (Asilus crabroniformis), belonging to the second division just mentioned. 
This insect is carnivorous, living 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 
manceuvre 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 aérial progress of the fly tribes, including the gad-flies (stride), 
horse-flies (Zabanide), carrion-flies (Muscide), 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 Qstrus 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.1 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 mancuvres 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 
Nicholson’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 ans 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 isnot 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, Manual of Ent. 463, 3 4to. iii, 86, 
2 Macquart, Dipteéres, i, 20, 191, 
