340 INSECTS INJURIOUS TO VEGETATION. 



the earth, thus carried away, is thrown into some pond-hole, and 

 left covered with water, many of the insects contained in it will 

 undergo their transformations and come out alive the next year. 



Canker-worms are subject to the attacks of many enemies. 

 Great numbers of them are devoured by several kinds of birds, 

 which live almost entirely upon them during their season.. They 

 are also eaten by a very large and splendid ground-beetle (CrtZo- 

 soma scrutator), that appears about the time when these insects 

 begin to leave the trees. These beetles do not fly, but they run 

 about in the grass after the canker-worms, and even mount upon 

 the trunks of the trees to seize them as they come down. The 

 latter are also stung by a four-winged ichneumon-fly, which de- 

 posits 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 succession, and swarms of them 

 may be observed around the trees as long as the canker-worms 

 remain. Their services, therefore, are doubtless very considera- 

 ble. Among a large number of canker-worms, taken promiscu- 

 ously 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 

 Nev^r-Haven, Connecticut, has made the interesting discovery 

 that the eggs of the canker-worm moth are pierced by a tiny 

 four-winged fly, a species of Platygaster, which goes from egg to 

 egg, and drops in each of them one of her own eggs. Some- 

 times every canker-worm egg in a cluster, will be found to have 

 been thus punctured and seeded for a future harvest of the Flaty- 

 gaster. 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 



