INSECT ENEMIES OF WESTERN FORESTS 73 



There is usually but one generation of these insects a year. Adult 

 moths appear in midsummer and deposit masses of eggs in bands 

 encircling small twigs. The eggs do not hatch until the leaves appear 

 the following spring. The young larvae feed on the new foliage, con- 

 struct the large tents on terminal branches, and reach maturity early 

 in the summer. They then form pupae, and the adult moths appear 

 soon after. 



Aside from the several species of predacious beetles and bugs that 

 feed on the caterpillars, there are parasitic insects that lay their 

 eggs within those of the moth, and the resulting minute larvae 

 develop wuthin the host eggs ancl destroy them. Further control is 

 accomplished by parasitic insects that breed within the caterpillars 

 and the pupae. Birds also play an active part in controlling the 

 tent caterpillar nuisance, many species feeding upon the caterpillars, 

 others feeding on the eggs, ancl still others, although to a lesser degree, 

 on the moths. Often the most complete control is accomplished by 

 a wilt disease that rapidly spreads among the colonies of caterpillars 

 and leaves but few survivors. 



There are six common species of tent caterpillars in the West, and 

 they are most easily distinguished in the field by the markings on 

 the caterpillars. 



The forest tent caterpillar {Malacosoina disstria Hbn.) is dusky 

 brown with a row of diamond or keyhole-shaped white spots along 

 the back and sides and with fine brown hairs. It feeds in large 

 colonies, without forming tents, on alder, birch, poplars, willows, 

 and a large number of broadleaved trees. They are distributed 

 generally over the United States. 



The eastern tent caterpillar (Malacosoma americana F.) has a 

 white line on the back, bordered with reddish brown, and on the 

 sides a row of blue spots and reddish-brown and yellow lines. It 

 feeds on various fruit, shade, and forest trees in the Eastern States 

 and is found in the Rocky Mountain region from New Mexico to 

 British Columbia. 



The California tent caterpillar {Malacosoma calif ornica Pack.) is 

 orange reel to brown above and paler brown below, with a blue line 

 on each side. This species is found in California, where it feeds on 

 ash, madroha, oak, willow, and other forest, shade, and fruit trees. 



The blue-sided tent caterpillar {Malacosoina constricta Stretch) has 

 an orange-brown body, with distinctly blue sides and blue dots along 

 each side of the center. It feeds on oak and other trees in Arizona, 

 California, and Oregon. 



The Great Basin tent caterpillar {Malacosoma fragilis Stretch) 

 (fig. 33) is distributed in the Great Basin region between the Rocky 

 Mountains and the Cascade-Sierra Nevada ranges, where it feeds on 

 bitterbrush, aspen, oak, poplar, willow, and other shrubs and trees. 

 The caterpillars of this species are distinguished by having a pale- 

 blue head and brown to black body, with a broad, pale-blue stripe 

 down the middle, fine orange lines on each side of the center, and 

 two blue spots on the sides of each segment. The hairs are whitish. 



The western tent caterpillar {Malacosoina pluvialis Dyar) (fig. 34) 

 is the common coastal species in the Pacific Northwest, that has as its 

 favorite food the alder, though feeding on other forest and fruit trees. 



