184 FARM FRIENDS AND FARM FOES 



If you stop to think, you can scarcely fail to wonder 

 how it was possible for one or even several mother flies 

 to lay so many eggs in a single caterpillar. Indeed, it has 

 been found that one fly probably cannot lay more than one 

 or two hundred eggs, and it would seem hard to believe 



that a dozen or more of 

 these flies laid their eggs 

 upon the Plusia caterpil- 

 lar all at once. But if 

 they did not do this, how 

 may we account for the 

 three thousand parasites ? 

 CHALCID" PARASITE OF GYPSY MOTH The observations of sev- 



EGGS eral European entomolo- 



gists indicate that the life 

 story of these parasites is something like this : 



The Plusia Moth lays its egg upon the cabbage leaf. 

 Shortly afterward the Chalcid Fly lays its egg within the 

 egg of the Plusia Moth. 



The Chalcid egg remains within the Plusia egg, so that 

 the latter hatches into a caterpillar with the unhatched 

 .Chalcid egg within its body. 



After a time the Chalcid egg hatches, but not into a 

 single larva. By a wonderful process its contents develop 

 into hundreds of tiny larvae that live on the body substance 

 of the Plusia caterpillar. They grow gradually inside 

 their caterpillar host. The latter finally dies, and the thou- 

 sands of parasites change to pupae within the skin. A 

 little later they change to flies. 



So, instead of the original egg developing into one Chal- 

 cid Fly as is so often the case, it develops into hundreds 

 if not thousands. Suppose a female Chalcid Fly laid an 

 egg in each of a hundred Plusia caterpillars, and each egg 



