134 ENTOMOLOGY 



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 structures for obtaining special food; indirectly, as in re- 

 spiratory 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 structures; active larvae, 

 as those of Carabidae, have an armor-like integument, but owe their pro- 

 tection from enemies chiefly to their powers of locomotion and their 

 aversion to light (negative phototropisni) ; 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 concealed 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, negative 

 reaction to light (negative phototropism) or a positive reaction to contact 

 (positive thigmotropism) . 



Exposed, sedentary larvae, as those of many Lepidoptera and Cole- 

 optera, often exhibit highly developed protective adaptations. Cater- 

 pillars may be colored to match their surroundings and may 

 resemble twigs, bird-dung, etc.; or larvae may possess a disagreeable 

 taste or repellent fluids or spines, these odious qualities being frequently 

 associated with warning colors. 



Larvae need protection also against adverse climatal conditions, 

 especially low temperature and excessive moisture. The thick hairy 

 clothing of some hibernating caterpillars, as Isia (Pyrrharctia) Isabella, 

 doubtless serves to mollify sudden changes of temperature. Naked 

 cutworms hibernate in well-sheltered situations, and the grubs of the 

 common "May beetles," or "June bugs," burrow down into the ground 

 below the reach of frost. Ordinary high temperatures have little effect 

 upon larvae, except to accelerate their growth. Excessive moisture is 

 fatal to immature insects in general conspicuously fatal to the chinch 



