18 CATERPILLARS AND THEIR MOTHS 



experiments with such larvae and their cells, and made 

 many observations, because some writers call these 

 cells " cocoons," but in only one cell which we have 

 seen — and we have examined many of many species 

 — has there been any trace of silk, and in none any 

 cohesion of the earthen walls of the cell which justi- 

 fies that name. Such as we have seen have been no 

 more like cocoons than is the hole a toad makes in the 

 earth, when it presses the walls of the hole smooth 

 and firm by moving around in it. 



Some caterpillars burrow in rotten or soft wood, 

 even in hard wood, or into pithy stems, fastening 

 themselves \n by spinning a door of silk across the 

 entrance-hole, while others spin loose webs of silk, like 

 fish-nets, among the fallen leaves on the ground. 



In these different shelters the caterpillars lie until 

 the pupa is formed in each, when the next change is 

 that which shall free the pupa from the now useless 

 larva-skin. The pupa presses against the head end of 

 the skin, and contracts and expands its body, as in 

 molting, until the skin bursts at the head end and is 

 cast as in molting ; it may be found in a neat little 

 wad in the bottom of a cocoon, or longer, moist, per- 

 haps inflated, in a cell, like a garment laid aside. In 

 both cases the skin has burst near the head, the head 

 itself often splitting down the median suture, and the 

 pupa has wriggled out as a soft, green, shapeless mass, 

 which soon settles into its pupa shape, becomes firmer 

 and brown, and is covered with a thin varnish formed 

 by the hardening of the fluid which was secreted be- 

 tween the larva-skin and the pupa and enabled the pupa 

 to push off the skin — " greased the ways," as it were. 



