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 obseryed 
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 Mor. 
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 ®shna 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 (Anaw 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 (shna variegata), very 
common in lanes and along hedges, which flies, like the Orthoplera, 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.? 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 Bphemera, 
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 fayourite, 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 neryures, there is every intermediate variety of reticulation that 
can be imagined.® 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. 5 Jurine, Hyménopt. t. 2—D. 
8 Entom, Mag. v. 251, 
