DIPTERA. 469 



in their habits to the true Ichneumon-flies. The chief parasite 

 of the pupa is the Cerapkrori destructor* of Say, a shining 

 bUxck four-wingctl fly, about one tenth of an inch in k^igth. 

 This has often been mistaken for the Hessian fly, from being 

 seen in wheat-fields, in vast numbers, and from its being found 

 to come out of the dried larva-skin of that fly. In the month 

 of June, when the maggot of the Hessian fly has taken the 

 form of a flax-seed, the Ceraphron pierces it, through the 

 sheath of the leaf, and lays an egg in the minute hole thus 

 made. From this egg is hatched a little maggot, which de- 

 vours the. pu})a 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 Platt/g-aster, that it is very abundant in the autumn, 

 when it lays its own eggs, four or five together, in a single egg 

 of the Hessian 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 cocoons 

 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 



* It is evident, from Mr. Say's description, and from Mr. Lesueur's figures, 

 that this insect is not a Ceraphron. Neither docs it belong to the genus Eury- 

 toma, to which I formerly referred it. It certainly comes very near to Pteromalus, 

 as suggested by Mr. Westwood ; but I apprehend that it should be placed in the 

 genus RhaphUe'us of Walker, or Storthyijocerus of Ilatzeburg. 



