Vol. XXviii] ENTOMOLOGICAL NEWS. 2Q5 



Life History and Habits of the Margined Water 

 Strider, Gerris marginatus Say (Hem., Het.). 



By J. R. DE LA TORRE BUENO, White Plains, New York. 



This species, Gerris marginatus, Say 1832, lacustris Kirby 

 1837 (sec. Van Duzee, Ch. L.), is the common smaller Gerris 

 spread over all the United States, a familiar form on ponds 

 and in the bays of lakes. It has been recorded in Canada from 

 British Columbia to Quebec, and in the United States from 

 Oregon and California to Georgia and Texas, but twenty- 

 three States are still to be heard from, including the greater 

 part of the Mississippi Basin. 



Gerris marginatus belongs in the subgenus Gerris sensu 

 strict n (Linmotrcchus) which contains the smaller members. 

 This subgenus, however, presents intergrading forms with 

 subgenus Aquarius among the exotic species, Gerris chilensis 

 Berg forming the passage. The character of the first joint 

 of the antenna shorter than the second and third taken to- 

 gether, in connection with the smaller size, serves to separate 

 Gerris from Aquarius. Two species of the subgenus in the 

 Eastern States may be confused with it, namely, Gerris buenoi 

 Kirkaldy and Gerris canaliculatus Say. The former is small- 

 er in size and has more pronounced abdominal sutures to- 

 gether with a flavescent marginal line on the anterior prothor- 

 acic lobe. The second species, while it may be larger or small- 

 er, has a distinctly more slender form and noticeably long and 

 slender legs and antennae. The genital character controls ; 

 it is well-figured by Parshley 1 . Weiss 2 experimented with G. 

 marginatus, apterous, as to orientation to water, or, using the 

 more technical expression, positive hydrotropism. He found 

 that up to 9 yards distant from a pond they immediately made 

 their way back : at 10 yards they began to experience difficulty ; 

 at 15, it increased, while at 30 or 40 yards they seemed to lose 

 their bearings, moved aimlessly about and after a time seemed 

 unable to find their way back to the water. The species is a 



Ent. News xxvii: 103, fig. b. 2 igi4- Can. Ent. : 33. 



