96 MISC. PUBLICATION 273, U.S. DEPT. OF AGRICULTURE 



38) is the common coastal species in the Pacific Northwest. Its 

 favorite food is the alder, though it also feeds on other forest 

 and fruit trees. The caterpillar is brown, with a row of elliptical 

 blue spots down the center and two orange spots on each segment. 

 On the sides are pale orange lines and spots. 



B 





4*> 



Figure 38. — The western tent caterpillar (Malacosoma pluvialis) : A, Egg- 

 mass on alder branch; B, full-grown caterpillar; C, cocoon webbed in 

 curled leaf; D, pupa; E, adult moths. All natural size. 



LOOPERS, SPANWORMS, OR MEASURING WORMS 



The leaf -feeding caterpillars of the (Geometridae) family of 

 moths infest a great many species and varieties of trees and 

 plants. Some species are among the most destructive defoliators 

 of forest trees. The caterpillars are smooth, nearly hairless, with 

 three pairs of true legs in front and two or three pair of prolegs 

 on the rear of the abdomen. These species can easily be recognized 

 by the characteristic way in which the caterpillars travel. They 

 move along by grasping with the hind pairs of prolegs while they 

 extend the body forward, then holding with the front legs while 

 they hump their backs to bring up their rear. This produces a loop- 

 ing motion, from which arises the common names of loopers, span- 



