68 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE 
found in dense clusters on the twigs, where they hibernate during 
the winter. In June the mature caterpillars spin cocoons, which are 
composed of silk and larval body hairs, and attached to the needles 
or twigs of the defoliated trees. In these cocoons they pupate. The 
species is distributed from Colorado to California and Oregon. 
Contro: measures under forest conditions are not likely to be 
justifiable. 
There are several closely related species of the genus which are 
also forest-tree leaf feeders. Halisidota ingens Hy. Edws. feeds on 
the needles of ponderosa and pinon pine in Colorado. Hf. maculata 
Harr. and its various varieties are found in all of the Western 
States, feeding on willow, oak, maple, alder, poplar, and a variety 
of other trees and shrubs. /. sobrina Stretch feeds on Monterey pine 
in California. 
The fall webworm (/7yphantria cunea Drury) is a common defoli- 
ator of broadleaved trees, such as madrona, alder, willow, cottonwood, 
and various other shade trees, fruit trees, and ornamentals, but it is 
of little importance from a forestry standpoint. The caterpillars, 
when full grown, are pale yellow to brown but appear grayish be- 
cause of the long whitish hairs that arise from black and orange 
tubercles. They : spin very large webs, within which they feed upon 
the fohage. 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 cocoons on the eround or attached 
to the tree trunks. The following spring the adult moths appear. 
These are nearly white, with a few black spots on the wings and 
orange markings on body and legs. A spotless form is called Z. 
textor Harris. 
The California oak worm (Phryganidia californica Pack.) (18) 
(fig. 31) periodically defoliates the various species of oaks in Cal 
fornia and sometimes attacks other trees in the vicinity of heavily 
infested oaks. It is particularly injurious to shade and ornamental 
oaks in the San Francisco Bay district, and not only renders the 
trees unsightly but may seriously weaken them or even cause their 
death. 
The moths have a body about one-half inch in length, and wings 
of light brown with darker veins and a spread of about 114 inches. 
The males are distinguished by having yellowish patches near the 
center of the forehead and by their broader and more feathery an- 
tennae. Full-grown caterpillars are about 1 inch in length, and of 
a dark olive green with conspicuous black and yellow longitudinal 
stripes on the ‘back and sides. 
The females lay eggs in groups of 2 to 40 on the under sides of 
oak leaves, on tree trunks, or other convenient places. The young 
caterpillars skeletonize the leaves, and later, as they reach full 
growth, consume all of the leaf. Two generations are produced each 
year. The moths fly in June and again in November. The winter 
is passed in the egg and early larval stages. 
Natural enemies include the spined soldier bug, a tachinid fly, and 
several species of wasplike parasites. A wilt disease takes a heav y toll 
of the caterpillars during epidemics. As a result of these natural 
control agencies, outbreaks occur only at irregular intervals. 
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