56 



HALF HOURS WITH INSECTS. 



[Packard. 



while those unattacked had preserved their fresh color, and 

 the tail moved about readily, the diseased ones becoming 

 stiff and more or less dried. Mr. Putnam thinks that at 

 least two-thirds of the chrysalides of this butterfl3% hundreds 

 of which had in the early autumn suspended themselves 

 about his house and fences, had been attacked by these 

 useful allies. 



On opening the bod}' of the infested chrysalides I found 

 about thirty parasites in different stages of growth, in one 

 case thirty-two, in another only twelve. We can readily see 



Fig. 44. 



Parasite of Cabbage Butterfly 



how efficient these minute insects become in reducing the 

 numbers of their hosts. A large proportion of the Ptero- 

 mali undoubtedly winter over in the body of the chrysalis, 

 the adult insects appearing in the spring. In England Mr. 

 Curtis found the fly in June, so that evidently there is an 

 autumn and spring brood of Chalcid flies. 



The male of this Pteroraalus is a beautiful pale-green fly, 

 with the body finely punctured and emitting metallic tints ; 

 the abdomen, or hind body, is flat, in dried specimens with 



24 



