358 MOTIONS OF INSECTS. 
tures 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 considerable diameter, thus rising spirally with 
arapid motion?. The object of these gyrations is pro- 
bably to increase her chance of meeting with a drone.—I 
have not much to tell you with respect tothe flight of other 
insects of this order, except that a spider-wasp (Pompzlus 
viaticus, F.) whose sting is redoubtable, and which often, 
when we are in the vicinity of sandy sunny banks, ac- 
companies 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 ter- 
minated by an oval, round, or triangular button, which 
seems capable of dilatation and contraction. The ani- 
mal moves these organs with great vivacity, often when 
at rest, and probably when flying. Their winglets 
(Alule) are different from those of Dytiscus marginalis, 
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 poisers, 
which, when the insect reposes, fold over each other 
like the valves of a bivalve shell ; but when it flies they 
* Huber, i, 38, 
