Insects in General 



quite closely; therefore the metamorphosis is said to be incomplete. 

 Grasshoppers, plant-lice and the true bugs are common examples of this 

 class. The young of these insects are called nymphs. 



The early forms of many insects, like the butterflies, moths, flies, 

 bees and beetles, differ so from the adults that there is no resemblance 

 whatever between the two. These insects pass through at least four 

 stages, the egg, larva, pupa and adult, each differing in form from the 

 other. For this reason their metamorphosis is said to be complete. 



The Egg 



The egg is the first stage in the development of any insect. The eggs 

 of some insects, like the plant-lice, remain in the abdomen of the mother 

 until the young are fully developed and hatched. Insect eggs vary 

 greatly in. form, as can be seen by referring to the figures given in the 

 Colored Plates. 



The Larva 



The larva is the form of an insect immediately following the egg. It 

 is then in the stage of growth, and many of our common insects damage 

 crops more severely during this period of their lives than at any other 

 time. Larvae differ greatly in form in the different orders. The larvae 

 of moths and butterflies are called caterpillars; those of flies are called 

 maggots; those of some beetles are called grubs and others worms. 

 Caterpillars are often called worms also. The legless larvae of bees, 

 wasps and related insects are sometimes called grubs. 



The Pupa 



The pupa is the third or resting stage. The larva becomes a pupa 

 when it has completed its growth. In this stage the insect has very little 

 or no power of movement, being unable to do more than wriggle the tip 

 of the abdomen at most. The pupa of a butterfly or moth is called a 

 chrysalis; the hardened larval skin within which the pupa of some two- 

 winged flies is formed is termed a puparium. 



The Adult 



The adult is the fourth and final stage in an insect's development. 

 No further growth takes place after this stage is reached. Only enough 

 food is taken by the adult to sustain life; in fact some adults do not feed 

 at all, their mouth parts having been lost through disuse. The prin- 

 ciple function of the adult is that of reproduction. 



The Integument 



The skin or integument of an insect is composed of a tough, horny 

 substance called chitin (pronounced ki-tin). At certain periods dur- 

 ing the larval stage this becomes so hard that it cannot stretch and soon 

 becomes too small for the growing insect. In the meantime a new skin 

 is forming underneath the old one, which splits open. The insect then 

 frees itself from its old coat. This process is called molting. The new 

 skin is at first soft and stretches to accommodate the increasing size of the 

 insect. Soon, however, it becomes hardened and must in turn be cast off. 

 Thus, in the course of their development insects shed their skins several 

 times. After reaching the adult stage molting ceases and all growth 

 stops. 



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