26 THE STUDY OF INSECTS 



The pupa. — This is the third stage in the life of many insects, and is 

 ordinarily a period of inaction, except that rapid and wonderful changes 

 go on within the body. Very few pupae, like those of mosquitoes, arc 

 active. Usually pupa? have no power of moving around, but many of 

 them can squirm when disturbed. When the last skin of the larva is 

 thrown off the pupa is revealed ; it is an oblong object, and frequently 

 apparently headless and footless. In many pupae the skin is a shiny 

 covering like porcelain. If a pupa be examined closely the antennas and 



legs and wings may be seen ; these are folded 

 up closely and soldered to the breast in the 

 case of the moths and butterflies (Fig. 50), 

 but free in case of the bees, ants, and 

 beetles. 



The chrysalis. — This term is often ap- 

 plied to the pupa of a butterfly. The word 



Fig. 50. - A pupa of a large moth. fe derived from a Q reek WQrd mcan ing gold, 



and came into use because of the golden dots and markings on many of the 

 butterfly pupae. 



The cocoon. — Many larvae, especially those of moths, when full 

 grown, spin about the body a silken case, so that when they change to 

 helpless pupae they may be protected from enemies, and from rain and 

 snow; these silken cases are called cocoons. They are frequently made 

 within a rolled leaf (Fig. 51), or beneath grass and rubbish on the ground, 

 or in cells below the ground. Some hairy caterpillars make cocoons 

 largely of their own hairs, which they fasten together with a film of silk. 



The important characteristic of 

 insects having a complete metamor- 

 phosis is that the wings develop in- 

 ternally. The wings begin to form in 

 the young larvae, caterpillars of but- 

 terflies, as buds of the hypodermis 

 underneath the cuticula and appear 

 for the first time when the last larval ^ 

 skin is shed. ( 



Imago. — A fully developed or „ J , . 



-. ,, . , . 11 j • TM Fig. 51. — A large cocoon wit hm a rolled leaf. 



adult insect is called an imago. I lie 



imagos of most insects except those of the orders Thysanura and.Col- 

 lembola have wings although there are many eases where wings have 

 been lost through disuse. An insect never grows or molts after it reaches 

 the adult stage. There is a popular belief that a small fly will grow into a 

 large fly, but this is not true, for after any insect gets its perfect wings it 

 can grow no larger, except that in case of females the body may be 

 distended by the growth of eggs within it. While many adults cat more 

 or less, it is only to sustain life, and not for growth. Indeed, many adult 

 insects take very little food, and some have lost their mouth-parts 

 entirely, through disuse. The adult stage usually lasts for a considerably 

 shorter time than the larval or nymph stages. In fact, it seems planned 

 in the economy of nature that the grown-up insects should live only long 

 enough to lay eggs, and thus secure the perpetuation of the species. For 

 example, mayflies live but a few days or even but a few hours, — just long 

 enough, apparently, to lay their eggs and provide for the perpetuation of 

 the species. 



