294 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I37 



extent. The level of significance in terms of predator evasion and 

 racial advantage is impossible to assess. However, some light on the 

 matter may come from measurements of the startle response time and 

 determination of that fraction of it which is occupied by nerve im- 

 pulse conduction. 



THE STARTLE RESPONSE TIME 



The competition between prey and predator is the oldest game in 

 the world. It must be the prototype of most man-made contests for 

 two, and like them contains a reasonable chance for either competitor 

 — an inevitable condition if both races are to survive. Unfortunately 

 there appears to be no available analysis of the odds and hazards to 

 each party in any prey-predator contest, but a significant factor in 

 this contest must surely be the strike time of the predator and the 

 startle time of the prey. Further, the selective advantage of a short 

 time to both parties might be expected to reduce these time intervals 

 to a minimum value which would be similar in both cases. Since the 

 predator in one contest is often the prey in another the strike and 

 startle times in widely differing animal groups might affect each other, 

 and hence might reach similar minimum values. It is admitted that the 

 singling out of a single factor such as reaction time from a complex 

 and little understood relationship is a highly questionable procedure. 

 Many other factors, such as relative numbers of prey and predator, 

 must play a major part in balancing the contest. Nevertheless, it pro- 

 vides an excuse for considering data on startle response times in 

 insects. 



Such data are scarce, and there does not appear to be any available 

 in relation to a specific predator. Treat (1955, 1956) used a kymo- 

 graphic method to register the interval between the onset of an ultra- 

 sonic stimulus and the change in flight pattern shown by various 

 noctuid moths. Tests on 14 females and 27 males of Graphiphora 

 c-nigrum L. gave a range of startle times of 75 to 262 msec, (milli- 

 seconds) with an average of 139 msec. 



A well-known response in insects which falls into the same cate- 

 gory as startle reactions is the tarsal flight reflex (Fraenkel, 1932; 

 Chadwick, 1953) in which movements of the wings follow loss of 

 tarsal contact. In the course of studies of the electrical and mechanical 

 events accompanying excitation of insect flight muscle (Roeder, 1951) 

 the onset of these events was determined oscillographically when a 

 platform was suddenly removed from beneath the tarsi of a suspended 

 insect (pi. 4, fig. 2). A reexamination of the records obtained during 



