INSECT METAMORPHOSIS 



is undoubtedly an advantage to a larva, especially to 

 such species as live in narrow spaces, or that burrow into 

 the ground or into the stems and twigs of plants; but 

 it probably just happened that the pupal stage was first 

 developed in an insect that had ingrowing wings. 



The typical larvae are the caterpillars, the grubs, and 

 the maggots, young insects with little or no resemblance 

 to their parents. The larvae of 

 some of the beetles (Fig. 137) and 

 of some members of the order 

 Neuroptera, however, are much 

 like the adults of their species, 

 except for the lack of external 

 wings and the compound eyes; 

 and even among the typical 

 larvae some species have more of 

 the adult characters than others. 

 The caterpillar (Fig. 136) or the 

 grub of the May-beetle (Fig. 131 

 B), for example, both being pro- 

 vided with legs, have a much 

 greater resemblance to an adult 

 insect than has the wormlike leg- 

 less grub of the wasp (Fig. 133 B) 

 or the maggot of the fly (Fig. 

 182 D). Hence, we see, the de- 

 gree of transformation may vary 

 much even among insects that 

 have a so-called "complete" 

 metamorphosis. 



There are a few insects that have no metamorphosis at 

 all. These are wingless insects belonging to the groups 

 known as Collembola and Thysanura (Figs. 57, 139, 140) 

 and are probably direct descendants from the primitive 

 wingless ancestors of the winged insects. These insects 

 during their growth shed the skin at intervals, but they 

 do not undergo a change of form; they illustrate the 



I ^-47 ) 



Fig. 139. Springtails, mem- 

 bers of the Order Collembola, 

 insects perhaps directly de- 

 scended from the unknown 

 wingless ancestors of winged 

 insects 



