INSECT ENEMIES OF WESTERN FORESTS 63 
Flight of the butterflies occurs in August, September, and October, 
and emerald- green eggs are laid on the needles a few hours after 
mating. These eggs are attached to needles near the tops of the 
trees and are laid in rows at an angle of 45°, with from 5 to 20 eggs 
in each row, and are firmly cemented together (fig. 28). The winter 
is passed in the egg stage, and the eggs hatch the following June, 
or about the time the new needles begin to appear on ponderosa pine. 
The larvae, as they hatch from the eggs, are very small, pale-green 
caterpillars, with shiny black heads. The young larvae feed in 
clusters, encircling the needle with their heads pointed toward the 
tip, forming a little ring of tiny black heads. Later on they feed 
FIGURE 28.—Progressive stages of the pine butterfly. (Drawings by Edmonston.) 
singly and reach maturity by the latter part of July. When mature 
they are approximately 1 inch long, dark green, and covered with 
fine, closely set hairs, and with two white lateral stripes down each 
side. The anal shield is produced behind into two blunt, well- 
separated projections. The head is pale green and covered with 
short hairs. The full-grown larvae lower themselves to the ground 
by silken threads and then ascend low- growing vegetation to trans- 
form to pupae, forming chrysalids attached to shrubs, g grasses, limbs, 
and tree trunks. From 15 to 20 days are spent in the pupal stage, 
and then the insects emerge as mature butterflies. Normally there is 
one generation a year. 
Outbreaks of the pine butterfly seldom last for more than 3 or 4 
years, for nature has provided a wasplike parasite (Zheronia ful- 
vescens Cress.) which was apparently responsible for the reduction 
of past outbreaks of this destructive pest. In the recent outbreak 
in central Idaho, it was found that during the third year of the 
epidemic over 90 percent of the caterpillars were parasitized by this 
