4 Bulletin of the Brooklyn Entomological Society Vol. XV 



species Gerris remigis are observed to be crowded into such iso- 

 lated pools also, but in far greater numbers than the former 

 species. 



As is well known, Gerris remigis includes both alate and apter- 

 ous forms, and it is possible that some of the macropterous indi- 

 viduals migrate by flight just previous to, and immediately after 

 the isolated pool stage is reached. I have no absolutely authentic 

 evidence that this occurs, but it is possible, for I have thought, 

 during certain seasons, that there seemed to be some decrease in 

 their numbers at such times, although, according to my observa- 

 tions, the alate forms are very few at any time. During those 

 seasons/when I have found a sufficient number of alate individ- 

 uals of Gerris remigis to make the effort at all worth while, I 

 have tried to obtain more data on this matter by attempting both 

 to count them and to estimate them, from day to day, on the sur- 

 face of various pools, from a number of different brooks. I 

 regret to state that the results were not very satisfactory. It is 

 a difficult proceeding, as anyone attempting to undertake it will 

 very quickly discover, because it is necessary to count all the 

 water-striders, both alate and apterous forms, in order to obtain 

 any exact quantitative information. While I did not achieve 

 definite results, it did seem, during some seasons, that there was 

 a slight reduction in the number of alate individuals at the 

 drought stages that I have mentioned. I wish to point out that 

 alate forms of Gerris remigis are found in the most unexpected 

 situations, frequently far from any permanent stream. It seems 

 difficult to explain their presence in such places, unless they have 

 migrated there by flight. 



When droughts are protracted, the isolated pools along the 

 channels of intermittent brooks become smaller and smaller. 

 Sometimes, during high temperatures and rapid evaporation of 

 the water, some of the alate individuals of Gerris marginatus mi- 

 grate, probably, by flight, as the water surface is reduced rapidly 

 in area. Certainly, they are fewer in numbers than is the case 

 at the beginning of such droughts, On perhaps three occasions, 

 when droughts of this character extended into the fall, I have wit- 

 nessed the flight of a few isolated specimens. I wish to state that 



