LEP1D0PTERA 



223 



Fig. 384. — A measuring-worm. 



Family Geometrid^ 



The Geometrids or the Measuring-worms 



The family Geometridae is composed of those moths the larvae of 

 which are known as measuring-worms, span-worms, or loopers. They 

 progress by a series of looping movements. 

 They first cling to the supporting twig or leaf 

 by their thoracic legs; then arch up the back 

 while they bring forward the hinder part of the 

 body and seize the support, at a point near the 

 thoracic legs, by the prolegs at the caudal end 

 of the body; then, letting loose the thoracic 

 legs (Fig. 384), they stretch the body forward, 

 thus making a step; this process is then re- 

 peated. 



The larvae of geometrids have as a rule only the last two pairs of pro- 

 legs well developed; and hence, as the middle part of the body is not 

 supported, they are unable to walk in the way that other caterpillars 

 walk. It is probable, however, that the loss of the first three pairs of 

 prolegs is the result of the looping gait rather than the cause of it. 



Frequently measuring-worms when resting cling by their prolegs and 

 hold the body out straight, stiff, and motionless, appearing like a twig; 

 this is doubtless a protective resemblance. 



The geometrid larvae are leaf-feeders, and some species occur in such 



large numbers as to be serious pests. 



The pupae are slender, and some 

 species are green or mottled in this 

 state. The pupa state is passed in a 

 very flimsy cocoon or in a cell in the 

 ground. 



The moths are of medium size, 

 sometimes small, but only rarely very 

 large. Usually the body is slender, 

 and the wings broad and delicate in 

 appearance. These moths occur on 

 the borders of woods and in forests, 

 rarely in meadows and pastures. 

 Their flight is neither strong nor long 

 sustained. Many species when at 

 rest hold the wings horizontally and 

 scarcely overlapping ; but other spe- 

 cies assume other positions, some 

 similar to butterflies. The type 

 of venation is shown in Figure 



385- . e 



There are many species of geom- 

 eters but the following are best 

 known. 



The fall canker-worm, Alsbphila 

 pometaria. — The canker-worms are 



Fig. 38;. — Wings of Caripela angusliorata. 



well-known pests, which are often very destructive to the foliage of fruit- 



