220 



they were the same kind of moths. As 

 in Cecropia the male moths are some- 

 what smaller than the females, and the 

 antennae show the same kind of dififer- 

 ences, i. e., the antennae of the males are 

 much larger and feather-like. In color, 

 the sexes of Cecropia are much alike, but 

 in this moth the differences in color are 

 very great, the dominant color in the fe- 

 male being a reddish brown, while that in 

 the male is a very dark-brown or almost 

 black. Thus these moths furnish an ex- 

 cellent illustration of what is called sexual 

 dimorphism, a term used for thoseanimals 

 in which the sexes are very different in 

 appearance, a subject to which Charles 

 Darwin gave considerable attention, in 

 his "Descent of Man." 



The female moth lays her cream-col- 

 ored eggs, which are a little smaller than 

 those of Cecropia, upon shrubs and trees 

 in clusters of five or six. The small larva 

 usually hatches in about ten days, and 

 feeds upon the leaves of ash, sassafras, 

 lilac, tulip tree, maple, cherry, and a num- 

 ber of other trees and shrubs, but it is 

 much more select in the choice of its food 

 than Cecropia. The larvae have voracious 

 appetites, devour many leaves and grow 

 at a correspondingly rapid rate. The dif- 

 ferences between the very young and the 

 adult larva, aside from that of size, are 

 very great. On account of_the very lim- 

 ited elasticity of the skin, this larva, like 

 other insect larvae, only increases in size 

 after shedding. This is periodically ac- 

 complished by throwing ofif the old skin, 

 which prevented expansion, and by grow- 

 ing a new and larger one. Promethea 

 has from three to five of these moults, the 

 number being influenced apparently by 

 climate, since southern larvae have more 

 moults than northern ones. The time be- 

 tween these moults varies from two days 

 to a week. 



The leaves upon which the larvae feed 

 may have long or short petioles. A 

 singular account has been given of how 

 these larvae have overcome the difficul- 

 ties associated with feeding upon long- 

 petioled leaves. There is considerable 

 risk of falling and of the leaf breaking 

 away when a large larva crawls out upon 

 a slender petiole. The larva avoids these 

 risks and yet reaches the blade of the leaf. 



This is accomplished as follows : The 

 larva grasps firmly the branch with its 

 posterior legs ; reaches out a considerable 

 distance along the petiole, and bites it 

 through in several places. This causes 

 the leaf to droop ; the larva now reaches 

 out, seizes the drooping leaf, and draws it 

 within convenient reach, where it can be 

 eaten at leisure. This is a wonderful dis- 

 play of instinct, yet it is not infallible, be- 

 cause at times the petioles are eaten too 

 far through, and when they droop, break 

 completely away and fall to the ground. 



When ready to spin its cocoon, the 

 adult larva is about two inches long; 

 these cocoons are very different from 

 those of Cecropia. As a rule, they are 

 found suspended from a branch by a silk- 

 en cord, the length of which depends up- 

 on the length of the petiole of the leaf in 

 which the cocoon was spun. Thus if the 

 leaf has only a short petiole, this cord is 

 also short, but if the petiole is two or 

 three inches long, the suspensory cord is 

 correspondingly long. The larva in con- 

 structing its cocoon, first spins a strong 

 band around a twig, and binds the petiole 

 of the leaf to the stem ; this band extends 

 down the petiole to the cocoon, and thus 

 anchors it. The cocoon proper, or the 

 part occupied by the chrysalis, is spun in 

 a folded leaf. When this leaf dies and 

 rots away, the cocoon hangs freely sus- 

 pended by the cord, but it is very evident 

 that the cocoon has been moulded in a 

 leaf by the prints of the veins which re- 

 main upon it. A valve-like opening oc- 

 curs in the upper end, through which the 

 moth emerges. 



The wings of the chrysalis are very 

 small as compared with those of the adult 

 moth ; are folded to the body on the under 

 side, and covered by the pupal skin. Dur- 

 ing the winter they remain transparent 

 since there are at this time none of the 

 rich colors present which are later found 

 in the moth. About ten days before the 

 moth emerges the wings become white, 

 a few days later definite colors begin to 

 appear on the under side of the wings 

 between the veins. While in the adult 

 moths the colors in the two sexes are 

 very distinct, at this time their wings are 

 vcrv similar. The wings do not long re- 

 tain this similarity, but gradually be- 



