MOTIONS OF INSECTS. 475 
generally bodies thicker than those of most other Hymenoptera, while those 
that have fewer nervures are more slender. This, however, does not 
hold good in all cases —so that the dimensions and cut of the wings, the 
strength of their nervures, and the force of their muscles, must also be 
taken into consideration. The wings of many of these insects, when 
expanded, are kept in the same plane by means of small hooks (amuti) 
in the anterior margin of the under wing, which lay hold of the posterior 
margin of the upper.! Another peculiarity also distinguishes them. Base 
cover's (tegule), or small concavo-convex shields, protect the base of the 
wings from injury? or displacement. 
The most powerful fliers in this order are the humble-bees, which, like 
the dung-chafers (Geotropes), traverse the air in segments of a circle, the 
are of which is alternately to right and left, The rapidity of their flight is 
so great that, could it be calculated, it would be found, the size of the crea- 
ture considered, far to exceed that of any bird, as has.been proved by the 
observations of a traveller in a railway carriage proceeding at the rate of 
twenty miles an hour, which was accompanied, though the wind was against 
them, fora considerable distance by a humble-bee (Bombus subinterruptus 
K.) not merely with the same rapidity, but even greater, as it not unfre- 
quently flew to and fro about the carriage or described zig-zag lines in its 
flight.’ The aérial movements of the hive-bee are more direct and leisurely. 
When leaving the hive for an excursion, I have observed that as soon as 
they come out they turn about as if to survey the entrance, and then, 
wheeling round in a circle, fly off. When they return to the hive, they 
often fly from side to side, as if to examine before they alight. When 
swarming, the heads of all are turned towards the group at the mouth of 
their dwelling; and upon rising into the air these little creatures fly so thick 
in'every direction, as to appear like a kind of net-work with meshes of every 
angle. The queen, also, upon going forth, when her object is to pair, after 
returning to reconnoitre, begins her flight by describing circles of consider- 
able diameter, thus rising spirally with a rapid motion. The object of these 
gyrations is probably to increase her chance of meeting with a drone. I 
have not much to tell you with respect to the flight of other insects of this 
order, except that a spider-wasp (Pompilus viaticus), whose sting is redoubt- 
able, and which often, when we are in the vicinity of sandy sunny banks, 
accompanies our steps, has a kind of jumping movement when it flies. 
The next order, the Diptera, consists altogether of two-winged flies ; but, 
to replace the under wings of the tetrapterous insects, they are furnished 
with poisers, and numbers of them also with winglets. The poisers (halteres) 
are little membranaceous threads, placed one under the origin of each wing, 
near a spiracle, and terminated by an oval, round, or triangular button, 
which seems capable of dilatation and contraction. The animal moves 
these organs with great vivacity, often when at rest, and probably when 
flying. Their winglets (alule) are different from those of Dytiscus mar 
ginalis, and the moth before noticed. Like them they are of rigid membrane, 
and fringed ; but they consist generally of two concavo-convex pieces 
(sometimes surrounded by a nervure), situated between the wing and the 
1 Kirby, Mon. Ap. Angl. i. 96. 108. t. xiii. f. 195 
2 Thid.i. 96. 107. t. v. f. 8. dd. 
5 Philos. Mag., quoted in Burmeister’s Manual of Ent, 464, 
4 Huber, i. 38. 
