ENEMIES OF THE CANKER-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, 
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-flics, 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 
* Seo the history of this insect, and a figure of her cells, in the Boston Culti- 
vator, for July 15, 1848. 
Fig. 235. 
