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 within the host eggs and 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, and 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 (Afalacosoma 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 californica Pack.) is 
orange red 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, madrona, oak, willow, and other forest, shade, and fruit trees. 
The blue-sided tent caterpillar (M/alacosoma 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 (Mfalacosoma fragilis Stretch) 
(fig. 38) 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 (Afalacosoma 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. 
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