l66 ARTHROPODS : INSECTS. 



form a small tent between the forks of the branches. 

 As they grow, they enlarge the tent, surrounding it 

 with new layers. They feed at stated times, and return 

 to their tents when they have finished eating. In crawl- 

 ing from one twig to another they spin a silken thread, 

 to guide them back. They rest in their tents at noon 

 and in stormy weather. When full-grown, about the 

 middle of June, they leave the trees, separate, wander 

 about for a time, and at length, in a sheltered place, spin 

 their oval and loosely woven cocoons. The meshes are 

 filled with a thin paste, which becomes a yellow pow- 

 der. They remain chrysalides about fifteen days. 



Geometers, or Spanworms. 



The Geometers are Moths whose caterpillars seem to 



measure the surfaces over which they pass. They are 



obliged to move in this way, because 



they usually ha\'e onh' ten legs, six 



true legs on the fore part of the 



body, and four prop legs at the hind 



Fig. 2S4.- Geometer, extremity. Geometers live upon 



or Spanworm. 111 , , 



trees, and let themselves down to 

 the ground by a silken thread which they spin from the 

 mouth while descending. When not eating, many of 

 them stand on the hind legs, with the body extended, and 

 in this attitude may easily be mistaken for a twig. Often 

 when disturbed, they let themselves down, hang till the 

 danger is past, and then climb up by the same thread. 

 The Cankerworm Moth expands about an inch and 

 a quarter, and the wings are large, thin, and silky. 

 The females have no wings. The larvje, called Canker- 

 worms, the most destructive of insects, make their ap- 



