MOTIONS OF INSECTS. 



285 



wings, which are nearly equal in size, are a complete and 

 beautiful piece of net-work, resembling the finest lace, the 

 meshes of which are usually filled by a pure, transparent, 

 glassy membrane. In two of the genera belonging to this 

 tribe the wings, when the animal is at rest, are always ex- 

 panded, so that they can take flight in an instant, no previous 

 unfolding of these organs being necessary. In Agrion, the 

 other genus of the tribe, the wings when they repose are not 

 expanded. I have observed of these insects, and also of se- 

 veral others in different orders, that without turning they 

 can fly in all directions — backwards, and to the right and 

 left, as well as forwards. This ability to fly all ways, without 

 having to turn, must be very useful to them when pursued 

 by a bird. Leeuwenhoek once saw a swallow chasing an 

 insect of this tribe, which he calls a Mordella, in a menagerie 

 about a hundred feet long. The little creature flew with such 

 astonishing velocity — to the right, to the left, and in all 

 directions — that this bird of rapid wing and ready evolution 

 was unable to overtake and entrap it ; the insect eluding 

 every attempt, and being generally six feet before it. 1 In- 

 deed, such is the power of the long wings by which the dra- 

 gon-flies are distinguished, particularly in JEshna and Libel- 

 lula, and such the force of the muscles that move them, that 

 they seem never to be wearied with flying. I have observed 

 one of the former genus {Anax imperator Leach) sailing for 

 hours over a piece of water — sometimes to and fro, and 

 sometimes wheeling from side to side; and all the while 

 chasing, capturing, and devouring the various insects that 

 came athwart its course, or driving away its competitors — 

 without ever seeming tired, or inclined to alight. Another 

 species (JEslina variegata), very common in lanes and along 

 hedges, which flies, like the Orthoptera, in a waving line, is 

 equally alert and active after its prey. This, however, often 

 alights for a moment, and then resumes its gay excursive 

 flights. A Libellula, resembling this last insect, flew on 

 board the vessel in which Mr. Davis was sailing, Dec. 1 1 . 

 1837, when at sea, and the nearest land was the coast of 



1 Leeuw, Epist.6. Mart. 1717. 



