242 



COLLEGE ZOOLOGY 



Adult ^••i *^ 



COMPLETE METAMORPHOSIS 

 (June beetle) 



0«ii 



Pupa 



Complete Metamorphosis 



Orders: 



Coleoptera 



Diptera 



Hymenoptera 



Lepidoptera 



Siphonaptero 



Figure 141. An insect with complete metamorphosis, June beetle. 



men. It possesses 6 small simple eyes on the 

 head but no compound eyes. The green cab- 

 bage caterpillars resemble very closely the 

 leaves on which they feed and are therefore 

 difficult to detect by birds and other enemies 

 (probably protective coloration). 



When full grown (about 1V4 inches in 

 length), the caterpillars attach themselves 

 with a silken thread from their silk glands to 

 the underside of a leaf of the host plant or 

 beneath some other object. Butterfly cater- 

 pillars do not spin cocoons as many moth 

 caterpillars do. After a time the body be- 

 comes shorter and thicker; the skin splits 

 down the back and is pushed off at the 

 posterior end; and a greenish-colored pupa 

 is revealed (Fig. 143). The pupa does not 

 feed; but, within it, violent activity is going 

 on. The digestive system changes from one 

 fitted for solid food to one that can utilize 

 liquid food; the muscular system of the 

 crawling larva becomes modified for pur- 

 poses of flight; the nervous system is made 

 over; wings grow out from pads of larval 

 tissue; and the reproductive organs grow to 



maturity. For these purposes, fat stored up 

 by the larva is largely utilized. When this is 

 all accomplished, requiring about 10 days, 

 the pupal skin splits, the adult butterfly 

 emerges, spreads its wings, and after they 

 have become dry, flies away. The adult 

 butterfly possesses a long proboscis coiled 

 beneath the head that can be extended so 

 as to probe the corollas of flowers for nectar, 

 which is sucked into the food reservoir. 



Many variations occur in the 4 types of 

 metamorphosis just described. For example, 

 among the termites one caste contains 

 nymphs that are sexually mature; the naiads 

 of mayflies, dragonflies, damsel flies, and 

 stone flies are aquatic; the nymphs of grass- 

 hoppers, crickets, cockroaches, and chinch 

 bugs are terrestrial; the nymphs of the 

 "seventeen-year locust" live in the ground 

 for 13 to 17 years before becoming adult; 

 aphids may be ovoviviparous or oviparous, 

 and their eggs may be fertilized or may de- 

 velop without fertilization; the larvae of 

 many beetles are called grubs; many moth 

 caterpillars spin cocoons in which to pupate; 



