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76 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE 
to 1932, when 50,000 acres were involved and about 200,000,000 feet 
of hemlock timber destroyed. 
Although western hemlock is the preferred host, the caterpillars 
appear in countless thousands when an outbreak occurs and feed on 
any foliage at hand. Douglas fir, Sitka spruce, and western red 
cedar may be heavily attacked when in mixture with hemlock; 
also huckleberry, salal, and broadleaved forest shrubs and trees 
are frequently eaten. 
In fact, when the cater- 
pillars are exceptionally 
numerous, nothing 
green is left on the in- 
fested areas. 
The moths are light 
buff, with a wing ex- 
panse of about 1% 
inches. The forewings 
are marked with two 
wavy lines and the hind 
wings with one wavy 
line. They fly, mate, 
and lay eggs late in 
September and during 
October. The eggs are 
about the size of a pin- 
head, gray green or 
brown, and are attached 
to the moss on the tree 
trunks, or to twigs or 
branches. It is in this 
stage that the winter is 
passed, and the eggs 
hatch the following 
spring. The young lar- 
vae, which are about 
one-fourth inch in 
! cribs length, crawl up the 
FiGuRE 35—The hemlock looper (Hilopia Ascellaria var. tree trunks and start 
moh Natural ste DERE Gy vag SEAS oe aaa cos feeding on the young 
needles. The first feed- 
ing takes place in May, June, and the early part of July and 
is not particularly noticeable. However, from the middle of July 
to October the feeding of the caterpillars causes a heavily infested 
forest to turn yellowish red and then brown, as though scorched by 
fire. Late in summer the caterpillars feed on the foliage, clip off 
small twigs, crawl over the trunks, cling to shrubs, and drop by 
silken webs from the trees to the ground. These silken webs may 
become so abundant that the whole forest looks and feels like one 
big cobweb. When full grown, the caterpillars are about 114 inches 
long, green to brown, with diamond-shaped markings on the back. 
They drop to the ground in August and September and secrete them- 
selves in protected places, such as crevices of the bark or under 
debris on the ground, and there transform to pupae. 
