62 NATURE SKETCHES IN TEMPERATE AMERICA 



fall their cocoons drop to the ground where they remain until 

 late spring or early summer (June) when the moths finally 

 emerge. The polyphemus caterpillar is often the victim of 

 the ichneumon insect known as Ophicn macrurum; the latter 

 parasite laying its eggs on the skin of the caterpillar's body and 

 finally causing its death. 



Before reaching maturity this larva passes through five 

 different larval stages, or four moults; Trouvelot^ states that he 

 has observed six larval stages. Sometimes the eggs of the moth 

 are parasitized by the little parasitic insect, Telenomns sphingis. 

 In warm seasons when the summers are very long, there 

 appear to be two broods. 



The large, ochre-colored moth, whose wings expand over 

 five inches, is subject to great variation, as many as six varieties 

 being recorded. The moth, at about the middle of the fore- 

 wings, presents a transparent spot encircled with a very thin 

 edging of black. The front margin of the wings is gray, while 

 just behind it the ground color is often tinged with brown; 

 near the ba.se of the forewings are broken white lines, edged 

 outwardly with black or dark brown. There is a dark, curved, 

 clouded line that extends across the lower wings parallel with 

 the edge, and is continued on the anterior wings forward more 

 than half-way acro.ss. The hind wings are exquisitely marked, 

 bearing a conspicuous eye-like window near the middle, mar- 

 gined with dee{) black and inwardly reflecting a blue shading, 

 which disappears into the black. Darwin suggests that the eye 

 spots on the hind wings of moths are pierced by birds in their 

 attacks on these insects and thereby save the vital parts from 

 destruction. The geograjjhical range of this species is across 

 the entire continent of America, extending into Mexico. 



There are .several questions that present them.selves as we 

 review the above sketch of its life history. These resolve 

 themselves as follows: First, the cause of the seemingly great 

 abundance of this species; .second, the cau.se of the number 

 of varieties; third, the cau.se of its polyphagous habit, or ability 

 to feed on a great variety of food plants; fourth, the cause of 

 the wide distribution of the species. 



It is obvious that the abundance of this insect shows that 

 ^American \aturalist, Vol. I, 1867. 



