110 
DIPTERA. 
worms, and even small shell-fish. The family is a 
numerous one. 
I pass over the families of Loncliopteridcc , Platy - 
pezidce , and Pipunculidce , as the species are not in 
any way remarkable. 
The flies of the family Syrphidce are very numerous; 
they feed chiefly on the nectar of flowers, over which 
they hover hawk-like; such is the rapidity of their 
vibration that the wings are almost invisible ; if 
alarmed they dart away with amazing velocity, soon 
returning to the same place. 
One species ( Syrphus pyrastri) may be often seen in 
gardens ; it is a blackish blue with pale hairs ; on the 
abdomen are three interrupted yellow or whitish bands. 
The larvae of the Syrphidce are leech-like creatures in 
form, having generally a broad posterior extremity and 
a narrow flexible head ; they are for the most part pre¬ 
daceous in their habits, feeding on the plant-lice or 
aphides. I have often seen a Syrphus larva holding on 
high in his mouth a mischievous little plant-louse, so 
that these flies must be put amongst the gardeners’ and 
farmers’ friends. 
The species of the genus Eristalis are remarkable for 
the length of the tail in the larvm. The perfect insects 
are of large size, and resemble bees both in form and 
colour, for which they are often mistaken. Eristalis 
tenax is, perhaps, the species most generally known. 
The larvm or rat-tailed maggots live in stagnant water, 
in the filthiest of mud, and in sewers ; the tail is a kind 
of telescopic tube, and contains a double air-channel, 
which is the respiratory organ ; when the maggot is 
immersed in thick filthy mud the respiratory tail is ex- 
