70 MISC. PUBLICATION 273, U. 8. DEPT. OF AGRICULTURE 
for the light, hairy caterpillars can be easily picked up and carried 
by air currents for: long distances. When disturbed or when in 
search of food, the larger larvae lower themselves to the ground by 
silken threads and travel rapidly, but dispersion at this stage could 
only be for short distances at most. Pupation takes place within a 
eray cocoon made of silk mixed with larval hairs. These may be 
attached to the twigs, limbs, 
or trunks of trees or on the 
underbrush. These cocoons 
are sometimes formed in 
masses six or seven layers 
deep, and in such cases the 
moths from the lower ones 
are unable to emerge. 
The Douglas fir tussock 
moth (/lemerocampa pseu- 
dotsugata McD.) (2) (fig. 
32) is a defoliator of major 
importance in the Douglas 
fir and balsam fir forests 
of eastern Oregon, Wash- 
ington, and British Colum- 
bia, and in Nevada and 
Idaho. It was first dis- 
covered in British Colum- 
bia in 1918, where it was 
severely defoliating Doug- 
las fir, and since then local 
damage has been noted at 
several points. The species 
was not recorded from the 
United States until 1927, 
when an outbreak occurred 
in Nevada. Then in 1929 
several outbreaks were 
found in different sections 
Figure 32.—The Douglas fir tussock moth (Hemero- of Idaho ) northeastern 
v=. 
campa pseudotsugata): A, Female laying eggs Washinoton, and eastern 
on cocoon; B. larva; C, male moth; D, female 5 4 3 Seo 
moth. Natural size. Oregon. The epidemic in. 
the Colville National For- 
est, Wash., reached a peak in 1930, spread over many square miles, and 
killed at least 300,000,000 board feet of Douglas fir and balsam fir, 
The Douglas fir which was not killed outright by the defoliation 
subsequently succumbed in many cases to the ‘attacks of the Douglas 
fir beetle. These extensive killings have been followed by some 
- disastrous fires. 
The Douglas fir tussock moth shows a decided preference for 
Douglas fir and species of balsam fir and can increase to epidemic 
numbers only when feeding on these preferred host trees. It will, 
however, feed on other species of conifers when mixed with firs, 
and even on the underbrush. Defoliation first occurs at the tops of 
trees, and as this foliage is destroyed the caterpillars work down on 
the lower foliage. 
