INSECT ENEMIES OF WESTERN FORESTS 75 
pillars 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. T hey 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 looping motion, from which arises 
the common names of loopers, spanworms, inchw orms, or measuring 
worms. Adults are 
medium-sized, 
slight-bodied, and 
light-colored moths 
of which the hem- 
lock or oak looper 
isatypicalexample. 
The hemlock loop- 
er (Lllopia fiscel- 
lara Guen.) (85) 
(496) 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 2 Oi FicurE 34,—The western tent caterpillar (Malacosoma plu- 
follow that are fre- vialis): A, Egg mass on alder branch: B, full-grown cater. 
pillar; C, cocoon webbed in curled leaf; D, pupa; H#, adult 
quently swept by moths. All natural size. 
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 luqubrosa 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 
