170 



Elementary Principles of Agriculture 



they leave the tree and each individual spins a paper- 

 like case, called a "cocoon," in some sheltered place. 

 The adult moth emerges from the cocoon in a few 

 weeks, and lays the eggs as mentioned above. These 

 changes may be observed by bringing the almost mature 

 caterpillars into wire-screened cages. These caterpillars 

 are attacked by many parasites, birds, snakes, frogs, 

 and particularly by birds. The orchard should be in- 

 spected in the early spring for webs. 



238. "Wire-worms" are very com- 

 mon in fields. They are the larval stage 

 of various species of 

 night-flying beetles, 

 such as the click- 

 beetles. The adult lives on the 

 nectar obtained from flowers 

 while the larval stage lives in 

 the ground and thrives on the 

 roots, leaves, and stems of 



young plants " 



239. Plant -lice, or Aphids, 



are common everywhere. There 

 are many kinds, and all are 

 quite small. Plant-lice are soft- 

 bodied, usually green, like the 

 "green bug," but sometimes 

 colored red or black according 

 to the plant they are infesting. 

 Most of them are wingless, 

 though some of them will 

 have two pairs of transpar- 

 ent wings. They almost al- 

 ways occur in colonies, 



Fig. 109. A corn-plant growing 

 in a root-cage infested by 

 wire-worms and click-beetles 

 (from a specimen in the Cor- 

 nell Insectary). 



