88 MISC. PUBLICATION 273, U.S. DEPT. OF AGRICULTURE 



hairs. The forewings are reddish brown with numerous distinct 

 silvery-white spots. The hind wings are light tan to nearly white 

 with a few brown marks near the outer margin. The moths 

 emerge, fly, and mate during July and August, and deposit pea- 

 green eggs in clusters on the twigs and needles of the host trees. 

 As many as 325 eggs have been laid by one moth. The eggs hatch 

 in about 2 weeks, and the small brown, hairy caterpillars feed in 

 dense clusters on the needles of lateral branches, forming webs 

 with masses of dead needles attached to the branches. Feeding 

 continues during the fall, the larvae hibernate in the webs during 

 the winter, then resume their gregarious feeding in the spring. 

 Late in the spring, the two-thirds-grown caterpillars disperse and 

 feed singly on the needles until mature. Full-grown caterpillars 

 are about iy 2 inches long, densely clothed with long brown-to-black 

 brushlike, poisonous hairs. In June the mature caterpillars spin 

 dirty-brown cocoons composed of silk and larval body hairs. They 

 attach the cocoons to the needles, twigs, or trunks of the defoliated 

 trees or to debris on the forest floor. 



The principal host is Douglas-fir, but this insect also attacks 

 true fir, Sitka spruce, shore pine, and occasionally other conifers. 

 It is distributed from the Atlantic to the Pacific, and the western 

 form is found throughout the Western States. This species would 

 be seriously destructive were it not for its natural enemies, which 

 annually take a heavy toll of the caterpillars. Therefore applied 

 control measures are not likely to be necessary. The variety H. 

 argentata sobrina Stretch feeds on Monterey pine in California. 



Several closely related species of the genus Halisidota are also 

 forest-tree leaf feeders. H. ingens Hy Edws. has dark-brown 

 forewings with large white splotches; the hind wings are white, 

 and the body is covered with buff-colored hairs. Its caterpillars 

 feed on the needles of young ponderosa and pinyon in Colorado, 

 Utah, New Mexico, and Arizona. 



The spotted tussock moth (Halisidota maculata (Harr.) ) has 

 tan forewings with wavy brown splotches and a spread of about 

 1% inches. The hind wings and body are buff -colored. The cater- 

 pillars, about iy 4 inches long, are densely covered with black hairs, 

 with a few white and yellow hairs intermixed and a wide belt of 

 shorter, tufted black hairs in their middles. This species and its 

 varieties are found in all the Western States feeding on willow, 

 oak, maple, alder, poplar, and many other trees and shrubs. 



The fall webworm (Hyphantria cunea (Drury)) is a common 

 defoliator of broadleaved trees, such as madrone, alder, willow, 

 cottonwood, and various other shade trees, fruit trees, and orna- 

 mentals, but it is of little importance to forestry. The caterpillars, 

 an inch long when full grown, are pale yellow to brown, but ap- 

 pear grayish because of the long whitish hairs that arise from 

 black and orange tubercles. They spin very large webs, within 

 which they feed on the foliage. These tents often enclose an entire 

 branch and are very conspicuous late in the summer. Feeding 

 takes place from July 1 to September 15. Maturity is reached late 

 in the fall, and the winter is passed as pupae in dark-brown co- 

 coons on the ground or attached to the tree trunks. The following 



