ENEMIES OF THE HESSIAN FLY. 
587 
egg is hatched a little maggot, which devours the pupa of 
the Hessian fly, and then changes to a chrysalis within the 
shell of the latter, through which it finally eats its way, 
after being transformed to a fly. This last change takes 
place both in the autumn and in the following spring. Some 
of the females of this or of a closely allied species come 
forth from the shells of the Hessian fly, without wings, or 
with only very short and imperfect wings, in which form 
they somewhat resemble minute ants. 
Two more parasites, which Mr. Herrick has not yet 
described, also destroy the Hessian fly, while the latter is 
in the flax-seed or pupa state. Mr. Herrick says, that the 
egg-parasite of the Hessian fly is a species of Platygaster, 
that it is very abundant in the autumn, when it lays its 
own eggs, four or five together, in a single egg of the Hes- 
sian fly. This, it appears, does not prevent the latter from 
hatching, but the maggot of the Hessian fly is unable to 
go through its transformations, and dies after taking the 
flax-seed form. Meanwhile its intestine foes are hatched, 
come to their growth, spin themselves little brownish co- 
coons within the skin of their victim, and, in due time, are 
changed to winged insects, and eat their way out. Such 
are some of the natural means, provided by a benevolent 
Providence, to check the ravages of the destructive Hessian 
fly. If we are humiliated by the reflection, that the Author 
of the universe should have made even small and feeble 
insects the instruments of His power, and that He should 
occasionally permit them to become the scourges of our race, 
ought we not to admire His wisdom in the formation of 
the still more humble agents that are appointed to arrest 
the work of destruction ? 
The wheat crops in England and Scotland often suffer 
severely from the depredations of the maggots of a very 
small gnat, called the wheat-fly, or the Cecidomyia Tritici 
of Mr. Kirby. This insect seems to have been long known 
in England, as appears from the following extract from a 
