392 ECONOMIC INSECTS 



stages of life during its existence: egg, larva, pupa and adult. 



All insects having complete metamorphosis have these four 

 stages of life. All the growth of the insect takes place during the 

 larva stage, although some feeding may also be done in the adut 

 stage. During the larva stage the insect moults, or sheds its skin, 

 several times to allow of increases in size. Instead of the outside 

 coat growing or stretching, it is cast off and a new and larger one 

 inside soon becomes hardened and when the insect is large enough 

 to fill it thjs in turn is cast off. 



The pupa stage is usually a resting or very quiet stage, Some- 

 times it is the winter stage of the insect, but often the pupa stage 

 is brief and is passed in the ground or other hiding place. During 

 this time the insect changes in structure and appearance a great 

 deal. New sets of internal organs are produced. The method of 

 digestion is sometimes changed. Rudimentary legs, wings and 

 other appendages are formed. Such complete change is made here 

 that the insect emerges from the pupa case as a very different in- 

 sect, so far as appearance and habits are concerned. The covering 

 of the pupa may be simply a leathery coat, or this may be covered 

 with a more or less hairy cocoon, as in the case of moths. 



When the adult insect emerges from the pupa case the rudi- 

 mentary appendages, such as the wings, are expanded and hard- 

 ened by exposure to the air, within a few minutes. The insect is 

 then full grown. No insects ever grow after reaching this stage. 

 Small flies never become large flies, and small butterflies never 

 become large butterflies. The adults of some species feed abun- 

 dantly, but in other species practically no food is taken during this 

 stage. In such cases the adult seems to exist chiefly for the pur- 

 pose of reproducing the species. After mating, suitable places are 

 found for laying eggs. A great instinct is exhibited in the search 

 for suitable places where the larvae when hatched from the eggs 

 may find proper food and surroundings. After the egg-laying 

 period is over the adults usually die. In some cases adults live 

 in a more or less dormant condition in secluded places through 

 the winter and lay their eggs in the spring. 



The chief orders or great groups of insects which have complete 

 metamorphosis and which are of great economic importance, are: 

 True beetles; butterflies and moths; flies and mosquitoes; bees, 

 ants and wasps. 



Incomplete metamorphosis differs from the complete type 

 in having no quiet or true pupa stage. The stage following 



