INSECT ENEMIES OF WESTERN FORESTS 79 



Key to Diagnosis of Injury from Defoliating Insects (Cont.) 



a. On conifers. 



(1) Caterpillars nearly naked with only fine 



hairs. 



aa. Dark-green caterpillars 1 inch long, 

 with fine, closely set hairs and 

 two lateral white stripes on each 

 side; on pines Pine butterfly, p. 80 



66. Caterpillars green to brown, with 

 three pairs of true legs in front 

 and two pairs of prolegs in the 

 rear, travel with a looping mo- 

 tion; mostly on hemlock 



Hemlock looper, p. 97 



(2) Caterpillars very hairy. 



aa. Caterpillars about 1 inch long, 

 brightly marked with blue, red, or 

 yellow spots and long pencils of 

 hairs — 2 in front and 1 in rear, 

 and with distinct tufts of hairs 

 like a toothbrush on their backs; 

 on firs Tussock moths, p. 90 



bb. Caterpillars of dull colors, black 

 and yellow, clothed with long fur- 

 like hairs; feeding in masses on 

 terminal branches. . . .Tiger moths, p. 87 



b. On broadleaved trees. 



(1) Caterpillars nearly naked with only fine 



hairs. 



aa. Traveling with a looping motion, 

 similar to hemlock looper; on oaks 

 from Oregon to British Columbia 



Oak looper, p. 100 



66. Olive-green caterpillars, about 1 

 inch long, with black and yellow 

 stripes on top and sides, brown or 

 red heads; California oaks 



California oakworm, p. 89 



(2) Caterpillars very hairy. 



aa. Caterpillars brightly marked with 

 long pencils of hairs in front and 

 behind and toothbrush-like tufts 

 of bristles on back 



Tussock moths, p. 90 

 66. Blackish caterpillars with row of 

 nearly square, white blotches 

 along the back, irregular white 

 marks along the sides, and brown 

 spines and longer, paler hairs; on 

 poplar and willow. . . .Satin moth, p. 93 

 3. Leaves chewed, and individual branches covered with dense 

 webbing; on broad-leaved trees 



Webworms and tent caterpillars, pp. 88, 94 

 a. Large, dense, conspicuous, silken tents formed at 

 end of branches or in crotches; made by lightly 

 haired caterpillars with blue, red, or yellow 



markings Tent caterpillars, p. 94 



6. Loosely woven tents formed at ends of branches; 

 made by yellowish-brown or gray caterpillars 

 clothed with long, white hairs; arising from 

 black and orange tubercles Fall webworm, p. 88 



