DIPTERA. —— SYRPHIDZ. 557 
nerved than those of the Muscide, having several perfect cells, the 
nerves closing the apical cells run parallel to the posterior margin of 
the wings ; the hind legs in many species are thickened and toothed. 
I have observed in some of the Helophili (whilst experimenting on the 
origin of the buzzing of these insects) an organ not hitherto noticed, 
connected with the thoracic organs of respiration, and the instruments 
whereby the buzzing is produced; this consists of a slender elongated 
filament clothed with very long and delicate hairs, fixed near the 
under side of the alula at its base, and at a little distance from the 
base of the balancer. 
These insects are either of a moderate or large size, and generally of 
variegated colours; they are very numerous, many species so much 
resemble humble bees, wasps, and other Diptera, that they are 
constantly mistaken for them by the inexperienced. In one genus, 
Volucella* (fig. 131. 2. Vol. mystacea), this similarity to the humble 
bees is of eminent service to the insects which deposit their eggs in 
the nests of those bees, an admirable provision of nature, since, as 
Messrs. Kirby and Spence observe, “Did these intruders venture 
themselves among the humble bees in a less kindred form, their lives 
would probably pay the forfeit of their presumption.” 
This family is of considerable extent, upwards of thirty genera, in- 
cluding more than 100 species, having been recorded as indigenous. 
In their perfect state they are particularly partial to flowers, especially 
such as are syngenesious. They fly with amazing rapidity, and many 
delight to hover immovably over certain spots, to which they will 
return, if disturbed for a considerable number of times. 
The typical genera are interesting on account of the peculiarity of 
their habits, the larvee feeding upon Aphides, amongst which the 
parent Syrphus has the instinct to deposit her eggs singly, so that the 
young are hatched in the midst of their food, which is soon devoured 
by these foes, which have but to extend their bodies in order to obtain 
a fresh victim. They are apodal grubs, destitute of eyes, and which 
have the mouth armed with a peculiar organ for suction, carefully de- 
scribed by Réaumur (fig. 130. 21. larva of Syrphus Pyrastri) ; when 
full grown, which takes place in summer in a short time, the larva 
* Saint Fargeau has made some interesting observations on the occasional con- 
nection of the opposite sexes of allied species of this genus, and the supposed pro- 
ductions of hybrid individuals resulting therefrom. (Encycl. Méth. tom, x. p. 785. ; 
Régne Animal, tom. v. p. 490. ; Bulletin Sci. Nat, Oct. 1828.) 
