INSECT BEHAVIOR 293 



the egg-shell are doubtless due to a sensation, probably one of temperature. 

 Simple contact with the egg-shell is probably sufficient to stimulate the 

 jaws to work, and the caterpillar eats its way out; yet it cannot foresee 

 that its biting is to result in its liberation. Nor, later on, when vora- 

 ciously devouring leaves, can the caterpillar be supposed to know that 

 it is storing up a reserve supply of food for the distant period of pupation 

 and the subsequent imaginal stage. The ends of these reflex actions are 

 proximate and not ultimate, except from the standpoint of higher in- 

 telligence. 



Just as simple reflexes link together to form an instinctive action, so 

 may instincts themselves combine. The complex behavior of a solitary 

 wasp is a chain of instincts, as the Peckhams have shown. All the opera- 

 tions of making the nest, stinging the prey, carrying it to the nest, etc., 

 are performed as a rule in a definite, predicable sequence, and even a 

 slight interference with the normal sequence disconcerts the insect. 

 Just as the performance of one reflex act may serve as the stimulus for 

 the next reflex in order, so the completion of one instinctive action may 

 be in part the stimulus for the next one. 



Modification of Instincts. An action can be regarded as purely 

 instinctive in its initial performance only, because every subsequent 

 performance may have been modified by experience; in other words, 

 habits may have been forming and fixing, so that the results of instinct 

 become blended with those of experience. Thus the first flight of a 

 dragon fly is instinctive and erratic, but later efforts, aided by experience, 

 are well under control. 



When once shaped by experience, reflex or instinctive actions tend 

 to become intense habits. Thus, certain caterpillars, having eaten all 

 the available leaves of a special kind, will almost invariably die rather 

 than adopt a new food plant, whereas larvae of the same species will eat 

 a strange plant if it is offered to them at birth. An act is strengthened 

 in each repetition by the influence of habit, to the increasing exclusion 

 of other possible modes of action. Many a caterpillar, having eaten its 

 way out of the egg-shell, does not stop eating, but consumes the remain- 

 der of the shell a reflex act, started by a stimulus of contact against the 

 jaws and continued until the cessation of the stimulus, unless some 

 stronger stimulus should intervene. It has been said that the larva eats 

 the remains of the shell because they might betray its presence to its 

 enemies. Whether this is true or not, to assume conscious foresight of 

 such a result on the part of an inexperienced caterpillar is worse than 

 unnecessary. 



