474 MOTIONS OF INSECTS. 



of the genera belonging to this tribe the wings, when the animal is at rest, 

 are always expanded, 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 several 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 Mar- 

 della, 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 direc- 

 tions 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 Indeed, such is the power of the long wings 

 by which the dragon-flies are distinguished, particularly in JEshna and 

 Libellula, 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 seem- 

 ing tired, or inclined to alight. Another species (JEshna 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 Libel- 

 lula, resembling this last insect, flew on board the vessel in which Mr. 

 Davis was sailing, Dec. 11. 1837, when at sea, and the nearest land was 

 the coast of Africa, 500 miles distant a striking proof of its powers of 

 wing. 2 The species of the genus Agrion cut the air with less velocity ; 

 but so rapid is the motion of their wings that they become quite invisible. 

 Hawking always about for prey, the Agrions, from the variety of the 

 colours of different individuals, form no uninteresting object during a 

 summer stroll. With respect to the mode of flight of the other neu- 

 ropterous tribes I have nothing to remark ; for that of the Ephemera, 

 which has been most noticed, I shall consider under another head. 



The next order of insects, the Hymenoptera, attract also general atten- 

 tion as fliers, and from our earliest years. The ferocious hornet, with its 

 trumpet of terror ; the intrusive and indomitable wasp ; the booming and 

 pacific humble-bee, the frequent prey of merciless schoolboys; and that 

 universal favourite, the industrious inhabitant of the hive, all belonging 

 to it, are familiar to every one; and in summer there is scarcely a flower 

 or leaf in field or garden, which is not visited by some of its numerous 

 tribes. The four wings of these insects, the upper pair of which are 

 larger than the under, vary much in their nervures. From the saw-flies 

 (Serrifera), whose wings are nearly as much reticulated as those of some 

 Neuroptera, to the minute Chalcis and Psilus, in which these organs are 

 without nervures, there is every intermediate variety of reticulation that 

 can be imagined. 3 It has been observed that the nervures of the wings are 

 usually proportioned to the weight of the insect. Thus the saw-flies have 



1 Leeuw. Epist. 6. Mart. 1717. 3 Jurine, Hymenopt. t. 25. 



2 Entom. Mag. v. 251. 



