318 ENTOMOLOGY 



Instincts and Tropisms. We have already emphasized the fact 

 that an instinct is a reflex act or a combination of reflex acts. The same 

 fact may now be stated in these words: an instinct is a tropism or a 

 combination of tropisms. The more important of these tropisms have 

 been considered. Whenever possible it is better to discard the ambigu- 

 ous term instinct in favor of such more precise terms as phototropism, 

 geotropism, etc.; though the term instinct remains useful as applied to an 

 action that is the resultant of several tropic responses. 



The modern student of instincts aims to resolve them into their 

 component reflexes and to determine as precisely as possible the influ- 

 ence of each reflex component. Thanks to the labors of a great number 

 of skilled investigators, we are no longer satisfied to class an action as 

 " instinctive" and then dismiss it from thought; for we are now in a 

 position to analyze the action, and may hope to explain it eventually 

 in terms of the physical and chemical properties of protoplasm. 



3. INTELLIGENCE 



Though manifestly dominant, pure instinct fails to account for all 

 insect behavior. The ability of an insect to profit by experience indi- 

 cates some degree of intelligence. 



Take, for example, the precision with which bees or wasps find their 

 way back to the nest. This is no longer to be accounted for on the as- 

 sumption of a mysterious "sense of direction," for there is the best of 

 evidence for believing that it depends upon the recognition of surround- 

 ing objects. When leaving the nest for the first time, these insects make 

 " locality studies," which are often elaborate. Referring to a digger- 

 wasp, Sphex ichneumonea, the Peckhams write: " At last, the nest dug, 

 she was ready to go out and seek for her store of provision and now came 

 a most thorough and systematic study of the surroundings. The nests 

 that had been made and then deserted had been left without any 

 circling. Evidently she was conscious of the difference and meant, 

 now, to take all necessary precautions against losing her way. She 

 flew in and out among the plants first in narrow circles near the surface 

 of the ground, and now in wider and wider ones as she rose higher in the 

 air, until at last she took a straight line and disappeared in the distance. 

 The diagram [Fig. 298, A] gives a tracing of her first study preparatory 

 to departure. Very often after one thorough study of the topography 

 of her home has been made, a wasp goes away a second time with much 

 less circling or with none at all. The second diagram [Fig. 298, B] gives 

 a fair illustration of one of these more hasty departures. 



