I 



RELATION BETWEEN PREY AND PREDATOR — ROEDER 303 



size, or movement of the prey must determine whether the predator 

 shows offensive or defensive behavior and must finally release the 

 strike (Rilling, unpublished thesis). Relative numbers of prey and 

 predator, and the degree to which the odds for survival of either con- 

 testant are affected by the outcome, must also play a part. In these 

 areas the neurophysiologist soon finds himself out of his depth. He 

 can only point out that, when compared with contestants in a man- 

 made game, the nervous systems of the insect contestants are relatively 

 simple, and that the outcome has surely been subjected to intense 

 natural selection. Students of evolutionary mechanisms, ethologists, 

 and game theorists might find common and fertile ground in a study 

 of the contest of the mantis and the fly. 



SUMMARY 



1. The small size of insects and inherently slow impulse conduction 

 in their unmyelinated nerve fibers impose a parsimony or economy of 

 nerve units in their nervous systems. It appears to be necessary that 

 relatively large (and therefore few) nerve fibers mediate neural events 

 in startle responses and predator evasion if insects are to be capable 

 of response times of the same order as those of their vertebrate 

 predators. This means that the neural components of startle mecha- 

 nisms occupy an amount of central nervous space disproportionate to 

 their complexity. 



2. This is illustrated by a description of portions of the neural 

 mechanisms concerned in startle responses in noctuid moths, locusts, 

 and cockroaches. 



3. The tarsal flight reflex of flies and the startle responses of 

 noctuid moths, cockroaches, and man all show similar response times 

 which may be causally related. 



4. An analysis of the times occupied by the sequence of neural 

 events occurring during the startle response of the cockroach shows 

 that about lo percent of the total response time is occupied by impulse 

 conduction in axons. 



5. The neural processes in the predator while locating, identifying, 

 and stalking its prey must be much more complex than this. This is 

 illustrated by a discussion of prey orientation in the praying mantis. 

 In the mantis the final stage of the attack, the strike, occupies about 

 the same time as the startle response of the potential prey. 



