GROWTH AND TRANSFORMATIONS OF INSECTS 49 



the adult insect emerges, with wings soft and limp but expand- 

 ing and hardening in a few hours, when it is ready to seek food 

 and a mate. 



Thus the stages of growth of those insects having a complete 

 metamorphosis are essentially different from those having the in- 

 complete type, as indicated in the following summary : 



Incomplete metamorphosis : Egg, Nymph, Adult. 

 Complete metamorphosis : Egg, Larva, Pupa, Adult. 



An insect never grows after it reaches the adult stage. The 

 little flies which appear on the window in early spring are not 

 'baby" flies and do not grow larger, but are entirely different 

 from other larger species 

 which supersede them 

 later in the season. 



The life histories of 

 insects are as diverse as 

 are the species, no two 

 being quite alike. To 

 study and carefully deter- 

 mine the time, place, 

 and manner of the trans- 

 formations is one of the 

 most important duties 

 of the economic ento- 

 mologist, for by ascer- 

 taining them the means 

 of control of injurious 

 species are often dis- 

 covered. Many insects 

 may thus be controlled 

 by simply changing gen- 

 eral farm methods, such 

 as the rotation of crops, 

 the time of plowing, etc., which result in the prevention or miti- 

 gation of the pest ; or a knowledge of the feeding habits may indi- 

 cate the most promising means of attack, and successful methods 

 may be determined by subsequent experiments. 



FIG. 61. Chrysalis of black swallow-tailed butterfly 

 (Papilio polyxenes] 



Showing attachment of tip of abdomen to mass of silk 



threads which have become torn from around the 



stem, and the silken loop which supports the thorax. 



(Photograph by Weed) 



