1 66 ENTOMOLOGY 



developed sense organs, excellent powers of locomotion, spe- 

 cial protective and aggressive devices, etc. In insects as a 

 whole, the environment of the larva or nymph and that of the 

 adult are very different, as in the dragon fly or the butterfly, 

 and the larvae are modified in a thousand ways for their own 

 immediate advantage, without any direct reference to the 

 needs of the imago. 



The chief purpose, so to speak, of the larva is to feed and 

 grow, and the largest modifications of the larva depend upon 

 nutrition. Take as one extreme, the legless, headless, fleshy 

 and sluggish maggot, embedded in an abundance of food, and 

 as the other extreme the active and " wide-awake " larva of 

 a carabid beetle, dependent for food upon its own powers of 

 sensation, locomotion, prehension, etc., and obliged meanwhile 

 to protect or defend itself. Between these extremes come 

 such forms as caterpillars, active to a moderate degree. The 

 great majority of larval characters, indeed, are correlated with 

 food habits, directly or indirectly; directly in the case of the 

 mouth parts, sensory and locomotor organs, and special struc- 

 tures for obtaining special food; indirectly, as in respiratory 

 adaptations and protective structures, these latter being numer- 

 ous and varied. 



Larvae that live in concealment, as those that burrow in the 

 ground or in plants, have few if any special protective struc- 

 tures ; active larvae, as those of Carabidae, have an armor-like 

 integument, but owe their protection from enemies chiefly to 

 their powers of locomotion and their aversion to light (nega- 

 tive phototropism) ; various aquatic nymphs (Zaitha, Odonata) 

 are often coated with mud and therefore difficult to distin- 

 guish so long as they do not move; caddis worms are con- 

 cealed in their cases, and caterpillars are often sheltered in a 

 leafy nest. There is no reason to suppose that insects conceal 

 themselves consciously, however, and one is not warranted in 

 speaking of an instinct for concealment in the case of insects 

 since everything goes to show that the propensity to hide, 

 though advantageous indeed, is simply a reflex, inevitable, 



