ENEMIES OF THE CANKEK-WORM. 471 



fraterna), an insect rather smaller than the common brown 

 wasp, fills her clay cells with canker-worms, often gathering 

 eighteen or twenty of them as food for her young.* A four- 

 winged ichneumon-fly also stings them, and deposits an egg 

 in every canker-worm thus wounded. From the egg is 

 hatched a little maggot, that preys on the fatty substance 

 of the canker-worm, and weakens it so much that it is 

 unable to go through its future transformations. I have 

 seen one of these flies sting several canker-worms in suc- 

 cession, and swarms of them may be observed around the 

 trees as long as the canker-worms remain. Their services, 



O ' 



therefore, are doubtless very considerable. Among a large 

 number of canker-worms, taken promiscuously from various 

 trees, I found that nearly one third of the whole were 

 unable to finish their transformations, because they had been 

 attacked by internal enemies of another kind. These were 

 little maggots, that lived singly within the bodies of the 

 canker-worms, till the latter died from weakness ; after which 

 the maggots underwent a change, and finally came out of 

 the bodies of their victims in the form of small two-winged 

 cuckoo-flies, belonging to the genus Tachina. 



Mr. E. C. Herrick, of New Haven, Connecticut, has made 

 the interesting discovery that the eggs of the canker-worm 

 moth are pierced by a tiny four-winged fly 

 (Fig. 235, greatly magnified), a species of 

 Platygaster, which goes from egg to egg, and 

 drops in each of them one of her own eggs. 

 Sometimes every canker-worm egg in a clus- 

 ter will be found to have been thus punctured and seeded 

 for a future harvest of the Platygaster. The young of this 

 Platygaster is an exceedingly minute maggot, hatched within 

 the canker-worm egg, the shell of which, though only one 

 thirtieth of an inch long, serves for its habitation, and the 

 contents for its food, till it is fully grown ; after which it 



* See the history of this insect, and a figure of her cells, in the Boston Culti- 

 vator, for July 15, 1848. 



