76 OUTLINES OF ENTOMOLOGY. 



In the process of growth, lepidopteroiis larvae moZ^ or change their 

 skins from three to five times. The operation is as follows : The 

 hindmost or anal pro-legs are made fast to some rough surface, or to a 

 mat of silk prepared for the purpose. The larva then rests and fasts 

 for a certain length of time. Presently the head plates begin to sepa- 

 rate from the neck, and a longitudinal slit appears on the top of the 

 thoracic segments, which gradually widens until the fore part of the 

 body can be forced through, after which, by alternate expansions and 

 contractions, the outgrown skin is made to slip backward until, by a 

 final effort, the anal legs are withdrawn and the crumpled mass of cast- 

 off skin, termed the exuvium (plural, exuvicej^ is left attached to the 

 leaf or bark, while the caterpillar, in its new dress — which is, in some 

 cases, quite differently colored and ornamented from the out-grown 

 one — crawls off in search of food with which to renew its exhausted 

 strength. 



The great majority of caterpillars subsist on the leaves, flowers and 

 fruit of trees, shrubs and herbaceous plants. Of these they consume 

 vast quantities every year, often partially or entirely destroying the 

 most valuable crops in satisfying their voracious appetites. A few 

 species infest drugs and gTocers' wares and some gnaw furs and woolen 

 goods. 



When full grown, caterpillars cease to feed, and seek some place 

 in which they will be concealed from their enemies while unable either 

 to escape or defend themselves. In this they succeed so well that it 

 is but rarely that the pupae are discovered by any but practiced eyes. 



Lepidopterous pupaj are called chrysalides. They are of various 

 shapes, some being angular and irregular in outline, and have the sur- 

 face roughened with humps and protuberances, while others are smooth, 

 oval or oblong and highly polished. The integument is horny or shelly 

 in its nature, composed of chitine, a substance which enters largely into 

 the composition of the body-wall of insects in all stages of develop- 

 ment. Each member is not encased in a separate sheath, as with the 

 Hymenoptera and Coleoptera, but the outlines of the parts can, in most 

 species, be distinguished through the case in which they are enclosed. 

 The chrysalides of many species have no covering or outer envelope, 

 but are simply attached by bands of silk to some surface. Others are 

 enclosed in thick cocoons, or hidden within roUed-up leaves, or formed 

 in earthen cells several inches under ground. The pupa state varies 

 in duration from eight or ten days to several months, according to the 

 habit of the species or the season of the year. 



