126 



ENTOMOLOGY 



2. EXTERNAL METAMORPHOSIS 



Metamorphosis. One of the most striking phenomena of insect 

 life is expressed by the term metamorphosis, which means conspicuous 

 change of form after birth. The egg of a butterfly produces a larva; 

 this eats and grows and at length becomes a pupa; which, in turn, de- 

 velops into an imago. These stages are so different (Fig. 27) that with- 

 out experience one could not know that they pertained to the same in- 

 dividual. 



Holometabola. The more specialized insects, namely, Neuroptera, 

 Mecoptera, Trichoptera, Lepidoptera, Coleoptera (Fig. 204), Diptera 



FIG. 204. Cyllene carycE. A, larva; B, pupa; C, imago. X 3. 



(Figs. 205, 29), Siphonaptera (Fig. 30) and Hymenoptera (Fig. 284), 

 undergo this indirect, or complete, 1 metamorphosis, involving profound 

 changes of form and distinguished by an inactive pupal stage. These 

 insects are grouped together as Holometabola. 



Larvas receive such popular names as "caterpillar" (Lepidoptera), 

 "grub" (Coleoptera), and "maggot" (Diptera), while the pupa of a 

 moth or butterfly (especially the latter) is called a "chrysalis." 



Heterometabola. In a grasshopper, as contrasted with a butterfly, 

 the imago, or adult, is essentially like the young at birth, except in hav- 

 ing wings and mature reproductive organs, and the insect is active 

 throughout life; hence the metamorphosis is termed direct, or incomplete. 



1 These terms, though somewhat misleading in implication, are currently used. 



