INSECT BEHAVIOR ' 359 



consumes the remainder 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. 



With insects, as with other animals, many instincts are 

 transitory ; even when partially fixed by habit, they .are replace- 

 able by stronger instincts. Thus the gregarious habit of lar- 

 vae is finally overpowered by a propensity to wander, which 

 does not mature, however, until the approach of the transfor- 

 mation period. The reproductive instinct is another of those 

 impulses that do not ripen until a certain age in the individual. 



Inflexibility of Instincts. Broadly speaking, instinctive 

 actions lack individuality are performed in the same way by 

 every individual of the species. The solitary wasps of the 

 same species are remarkably consistent in architecture, in the 

 selection of a special kind of prey, in the way they sting it, 

 carry it to the nest and dispose of it ; all these operations, more- 

 over, are performed in a sequence that is characteristic of the 

 species. Examples of this so-called inflexibility of instinct are 

 so omnipresent, indeed, that insect behavior as a whole is 

 admitted to be instinctive, or automatic. Insects are capable 

 of an immense number of reflex impulses, ready to act singly 

 or in intricate correlation, upon the requisite stimuli from the 

 environment. 



To normal conditions of the environment, the behavior of 

 an insect is accurately adjusted; in the face of abnormal cir- 

 cumstances, however, demanding the exercise of judgment, 

 most insects are helpless. The specialization to one kind of 

 food, though usually advantageous, is fatal if the supply be- 

 comes insufficient and the larva is unable to adopf* another 

 food. A species of Sphex habitually drags its grasshopper 

 victim by one antenna. Fabre cut off both antennae and then 



