INTRODUCTION. 11 



the wbb is thin and hardly conceals the surface, but some- 

 times it is almost like parchment, as in the J^Iexican 

 Euclieira social is. Winter is sometimes passed in one of 

 these webs, and when constructed, as it sometimes is, on an 

 annual, the shrinkage after the death of the stalk makes a 

 compact mass of leaves, frass, web, and caterpillars, from 

 which it would seem as if no caterpillar could escape in 

 the spring. When social caterpillars construct no shelter, 

 they usually feed side by side in rows, and move from place 

 to place in files. 



A very large number of our caterpillars live through the 

 winter, and this is often the only means by which a 

 species survives the inclement season; most of them hiber- 

 nate when about half grown; others, strange to say, jusc 

 from the egg, without having eaten anything but the shell 

 from which they came; still others hibernate full grown 

 and full fed, changing to chrysalis just when vegetation 

 starts in the spring. Some of these caterpillars, especially 

 those partly or fully grown, construct nests for hiberna- 

 tion; others use the same nest which has served their 

 larval life, strengthening it against the greater needs of 

 winter; others seek crannies of any kind. 



In some cases where the caterpillars of a second brood 

 hibernate when half-grown, the caterpillars of the first 

 brood at the hibernating age, but in midsummer, will fall 

 into letharg}^ from Avhich some will arouse after say a fort- 

 night's quiescence, while others AviH prolong their pre- 

 mature into actual hibernation, and in the following spring 

 caterpillars of the same stage but of two successive broods 

 will mingle together. 



It is apparent, then, that there is considerable variety 

 in the duration of life of caterpillars. Instances are on 

 record where the time from birth to chrysalis was only 

 about ten days; ordinarily it is at least a month; with 

 those that hibernate it may be in some cases nearly a year; 



