316 ENTOMOLOGY 



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 num- 

 ber 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; but in the face of abnormal circumstances 

 demanding the exercise of judgment, most insects are helpless. The 

 specialization to one kind of food, though usually advantageous, is fatal 

 if the supply becomes 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 antennae and then found that the 

 wasp, after vain efforts to secure its customary hold, abandoned the 

 prey. Under such unaccustomed conditions, insects often show a sur- 

 prising stupidity, capable as they are amid ordinary circumstances. 



Flexibility of Instincts. Notwithstanding such examples, the 

 common assertion that instincts are absolutely " blind," or inflexible, is 

 incorrect. Instinctive acts are not mechanically invariable, though 

 their variations are so inconspicuous as frequently to escape casual 

 observation. A precise observer can detect individual variations in the 

 performance of any instinctive act variations analogous to those of 

 structure. 



To take extreme examples, the Peckhams found that an occasional 

 queen of Polistes fusca would occupy a comb of the previous year, 

 instead of building a new one ; and that an individual of Pompilus mar- 

 ginatus, instead of hiding her captured spider in a hole or under a lump 

 of earth as usual, hung it up in the fork of a purslane plant. They 

 observed also that one Ammophila, in order to pound down the earth 

 over her nest, actually used a stone, held between the mandibles (Fig. 

 297). 



This performance, which has been witnessed also by Professor 

 Williston and a few other observers, illustrates the flexibility of in- 

 stinctive action, and has been cited as an instance of adaptability, or 

 intelligence. It can not be supposed, however, that the insect is 

 conscious of the efficiency of a stone as a tool. The performance may be 

 an accident. If one observes an Ammophila at work he will notice that 

 she not only pounds down the earth with her head, but also lifts and 

 lays aside small stones with her mandibles. Possibly she now and then 

 chances to begin the pounding movement before she has happened to 

 release a stone from her jaws. 



