Qg MISC. PUBLTCATIOX 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. 

 Control 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. Halmdota ingens Hy. Edws. feeds on 

 the needles of ponderosa and pihon pine in Colorado. II. 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. H. sohrhia Stretch feeds on jNIonterey pine 

 in California. 



The fall webworm {Hyphantria ciinea Drury) is a common defoli- 

 ator of broadleaved trees, such as madroha, 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 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 cocoons on the ground 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 H. 

 textor Harris. 



The California oak worm (Pliryganidia calif ornica Pack.) (18) 

 (fig. 31) periodically defoliates the various species of oaks in Cali- 

 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 li/4 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 Xovember. The winter 

 is passed in the ^gg and early larval stages. 



Natural enemies include the spined soldier bug, a tachinid fly, and 

 several species of wasplike parasites. A mlt disease takes a heavy toll 

 of the caterpillars during epidemics. As a result of these natural 

 control agencies, outbreaks occur only at irregular intervals. 



