82 MISC. PUBLICATION 273, U.S. DEPT. OF AGRICULTURE 



The adult is a white butterfly with black markings and a wing- 

 expanse of about 1% inches, resembling in general the common 

 cabbage butterfly. The wings of the male are white except for some 

 black markings on the tips. The forewings of the female have 

 similar black markings, but have a distinct yellowish cast; the 

 hind wings have the same yellowish cast but have a much heavier 

 black marking than in the male. Many, but not all, females, have 

 bright orange spots along the apical margin of the hind wings. 

 These butterflies may be seen nearly every year flying about in 

 pine and fir forests and hovering about the tops of trees. 



Flight of the pine butterflies occurs in August, September, and 

 October, and they lay emerald-green eggs 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, firmly cemented together (fig. 32). 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 pon- 

 derosa pine. The larvae, as they hatch, are very small, pale-green 

 caterpillars, with shiny black heads. They feed in clusters, en- 

 circling the needle with their heads pointed toward the tip, form- 

 ing a little ring of tiny black heads. Later on they feed 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-sepa- 

 rated 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, 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 (Theronia 

 fidvescens Cress.), which was apparently responsible for the re- 

 duction of past outbreaks of this destructive pest. In the 1922 

 outbreak in central Idaho during the third year of the epidemic, 

 over 90 percent of the caterpillars were parasitized by this bene- 

 ficial insect, and the following season it was practically impossible 

 to find a living caterpillar or butterfly within the defoliated areas. 

 Before natural control becomes effective, however, a great deal of 

 timber may be lost. 



Artificial control by airplane spraying may prove useful in pro- 

 tecting the forests from heavy defoliation during the peak of the 

 outbreak and until the defoliator is brought under control by 

 natural means. If even half the foliage of a tree could be saved, 

 the death of the tree would probably be prevented. 



GIANT SILK MOTHS 



The giant silk moths (Saturniidae) comprise a family of very 

 large moths, the caterpillars of which are armed with spines or 

 tubercles. Most of them spin dense silken cocoons in which to 



