INSECT ENEMIES OF WESTERN FORESTS 



75 



pillars are smooth, nearly hairless, with three pairs of true le^s 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 Avhile they extend the body forward, then 

 holding with the front legs while they hump their backs to bring 

 up their rear. This produces a looping motion, from which arises 

 the common names of loopers, spauAvorms, inchworms, or measuring 

 worms. Adults are 

 m e d i um-siz e cl, 

 slight -bodied, a n d 

 light-colored moths 

 of which the hem- 

 lock or oak looper 

 is a typical example. 



The hemlock loop- 

 er {EUopia fiscel- 

 laria Guen.) {85) 

 {JiBh) is a very de- 

 structive 'defoliator 

 in the spruce, hem- 

 lock, and balsam fir 

 forests of the North- 

 eastern States, 

 through Canada, 

 the Lake States, and 

 along the north- 

 western coast. At 

 intervals it appears 

 in great numbers, 

 strips the needles 

 from trees over 

 large areas and 

 causes their death. 

 These defoliated 

 trees become very 

 dry, and jungles of 

 fallen trees and 

 broken tops soon 

 follow that are fre- 

 quently sw^ept by 

 disastrous fires. 



The species that destroys the spruce-hemlock forests along the 

 coast of Oregon, Washington, and British Columbia has been re- 

 ferred to as the variety lugubrosa Hulst (fig. 35). During the last 

 40 years it has figured in three major outbreaks. The earliest out- 

 break of record occurred about 1889 to 1891, when a vast amount 

 of timber in Tillamook and Clatsop Counties, Oreg., and Grays 

 Harbor County, Wash., was destroyed. The second outbreak oc- 

 curred again in Tillamook County in 1918-21, when several town- 

 ships were affected and 500,000,000 board feet of hemlock and Doug- 

 las fir were reported to have been killed. The latest outbreak 

 occurred in Pacific and Grays Harbor Counties, Wash., from 1929 



Figure 34. — The western tent caterpillar {Malacosoma phi- 

 vialis) : A, Egg mass on alder branch: B, full-grown cater- 

 pillar ; C, cocoon webbed in curled leaf ; D, pupa ; E, adult 

 'moths. All natural size. 



