CH. III.] INSECTS WHICH FORM COCOONS. 71 



plant with considerable skill, side by side, the round- 

 ed figure formed by their union being larger at one 

 end than the other. 



Other caterpillars, like the humblebees, give to 

 their cocoons a covering of moss. One of these is 



a small smooth larva, with sixteen legs, which feeds 

 upon minute mosses or lichens, and which appears 

 to be that of the marbled green moth (Bryophila 

 glandifera.) This caterpillar forms a cocoon of a 

 rounded form, surrounded with moss, of which 

 small tufts are fastened together so as to form a 

 hollow ball. 



In general, the caterpillar enclosed in a cocoon 

 becomes a chrysalis in a few days ; but there are 

 some instances in which the caterpillar remains 

 unchanged for several months. 



When one of these cocoon-forming insects has 

 completed its state of inactivity in the chrysalis 

 state, it bursts out of the pupa in the same manner 

 as the butterflies. It has yet, however, another ef- 

 fort to make before it sees the light of day. It is 

 born in a dark prison, the walls of which are often 

 of the most surprising hardness, and the enclosed 

 animal is weak, and apparently unprovided with jaws 

 or other instruments to effect its escape. The man- 

 ner in which this is managed has not been quite 

 satisfactorily explained. Some authors have as- 

 serted that it is by the action of a powerful liquid 

 which the moth emits from the mouth, that the 

 threads of a cocoon are rendered moist and pliant, 



