SOME HABITAT RESPONSES OF THE LARGE 

 WATER-STRIDER, GERRIS REMIGJS 

 SAY. Ill 



C. F. CUKTIS RILEY 

 The New York State College of Forestry at Syracuse University, 



VI. Discussion of Experiments at White Heath 

 1. Role Played by Vision,— In regard to the experi- 

 ments at White Heath there is little to be said more than 

 already has been stated in the discussion in connection 

 with the responses of the water-striders, during severe 

 drought, in the dry bed of the stream. In general, the 

 majority of the gerrids found their way back to the brook, 

 when removed from it to distances of one, two, three, and 

 four yards. This was true whether they faced the brook, 

 were placed with their bodies parallel to its banks, or 

 faced directly away from the water. Water-striders with 

 their heads turned away from the stream took a little 

 longer time to reach the brook than was true of the other 

 hemipterons, and they also evinced more random move- 

 ments. Occasionally a gerrid wandered astray and 

 seemed unable to reach the brook. 



At such short distances away from the water, as have 

 been mentioned, it is very probable that the hemipterons 

 find their way back to it mainly through the sense of sight. 

 It is a well-known fact that many species of aquatic Hem- 

 iptera respond positively to light as a stimulus, indicating 

 that vision must play an important part in the behavior 

 of the members of this group. Among these are the 

 water-striders Gerris orba (Essenberg, 1915, p. 400), 

 Gerris remigis, Gerris marginatus (Riley, MS.), and prob- 

 ably Gerris thoracicus, Gerris tristan (Kirkaldy, 1899, 

 p. 110). Not only do certain water bugs respond posi- 

 tively to light, but Cole (1907, p. 387) has proved the truly 

 remarkable fact that Ranatra ftisca possesses the ability 

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