174 NORTH AMERICAN INSECTS. 



they may alight. They particularly infest these places, be- 

 cause there are so few of the birds there which feed par- 

 ticularly upon them. 



But the ravages of these insects are not confined to our 

 shade trees, for they feed also upon the leaves of our fruit 

 trees, as well as of elms, poplar, lime, and other trees. 

 When fully grown they are forced by nature to go to the 

 ground, in order there to undergo their metamorphosis into 

 a cocoon ; and as they are not provided with sixteen feet, 

 like other caterpillars, they are very poor pedestrians, and 

 find it much easier to let themselves down to the ground by 

 means of the silken thread which issues from their mouth 

 as they need it. They sometimes descend from a height 

 of more than fifty feet in a few moments, while, if they were 

 obliged to depend upon their ten, or, at most, twelve legs, 

 the journey would occupy them several days. 



Caterpillars generally have sixteen legs, or feet, placed at 

 equal distances along the under part of the body ; but these 

 have only five or six feet at each extremity, and none under 

 the middle, so that when they walk they stand on the hind 

 feet, and throw their fore feet and body as far ahead as its 

 length will allow ; then, standing on their fore feet, they draw 

 up the hind ones to them, making an arch of the footless 

 centre of the body. This process, it is evident, must be 

 slow ; and it is probably on account of this singular method 

 of locomotion, which resembles somewhat that of spanning 

 or measuring, that they received from Linnaeus the name 

 Geometrce, and from other authors the names " Measurers," 

 " Span-worms," and " Tailors." 



In the United States we find a great variety of these 

 caterpillars, all of which are in their season metamorphosed 

 into small moths, the most conspicuous of which is : 



The CANKER- WORM (Anisopteryx pometaria). The cater- 

 pillars of this moth are usually hatched from their eggs in 

 the spring, and when very young are of a dark-brown color, 



