20 



COLEOPTERA OF INDIANA. 



RELATIONS OF THE BEETLES OR COLEOPTERA TO OTHER 



INSECTS. 



All true insects can be separated into one of two great groups, 

 based upon the kind of changes or transformations which they un- 

 dergo before reaching the adult or winged stage. To one group, the 

 Heterometabola, belong those insects in which the metamorphosis 

 (or changes which they undergo after hatching from the egg) is in- 

 complete. In this group the young, when hatched, is of the same 

 general form as the parent, but wholly wingless. As the insect 

 grows it moults its skin a number of times and wings develop grad- 

 ually, there being no sharp line defining the larval and pupal stages. 

 The young of all stages are called "nymphs;" they continue active 

 and feed from the time of hatching until they reach the final moult 

 and emerge therefrom mature or in the imago stage. Familiar ex- 

 amples of the Heterometabola are the locust, grasshopper, katydid, 

 dragon-fly, squash-bug and chinch-bug. 



The second group, the Melabola, comprises those insects which 

 undergo what is termed a complete metamorphosis. In this group 

 there are four distinct stages— the egg, larval, pupal and imago— m 

 the order named. No insect is hatched from the egg with wings, 

 and when an insect reaches the winged stage it is adult, and never 

 grows thereafter. Thus the gnats and midges are not the sons and 

 daughters of the larger flies, but are full-grown insects of them- 

 selves, which are undergoing the fourth or last stage of their lives. 

 The second, the larval or worm-like stage, is the one in which the 

 insect of this group is commonly the most injurious, for then it eats 

 voraciously, and then is the only period of its life when it grows in 

 size. The pupal, or third stage, is usually a quiescent one, the in- 

 sect eating nothing and not increasing in size, but undergoing great 

 changes of form. Thus the homely and often repulsive grubs, mag- 

 gots and caterpillars, which are the larval forms of the beetles, flies 

 and butterflies, respectively, enter the third stage as worm-like, 

 crawling creatures, and emerge from it as beautiful winged forms, 

 sometimes glistening and gleaming with all the colors of the rain- 

 bow. This change of life and form is undoubtedly of great advant- 

 age to most of this group of insects, as it tends to prevent the ex- 

 tinction of the species ; since, if at a given moment the parents were 

 swept out of existence, the young, living in a different station, 

 would continue to represent the species. 



It is to this second group, the Metabola, whose members undergo 

 a complete metamorphosis, that the Coleoptera or beetles belong. 



