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- 
ve 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 1f the supply be- 
comes insufficient and the larva is unable to adopt another 
food. <A species of Sphex habitually drags its grasshopper 
victim by one antenna. Fabre cut off both antennze and then 
