2 Bulletin of the Brooklyn Entomological Society Vol. XV 



of the apterous migrating gerrids after the water in their hab- 

 itats has dried up entirely. Such droughts, extending over a 

 large region, are likely to cause the death of great numbers of 

 apterous individuals, and even may result in the extinction, dur- 

 ing a particular season, of any species represented by apterous 

 specimens solely. Kirkaldy,^ discussing some of the habitat re- 

 sponses of Gerris lacustris, makes the following statement with 

 respect to this subject: 



In small wayside pools or streamlets which dry up period- 

 ically, it is obvious that the apterous inhabitants will die out unless 

 their habitat is sufficiently near to a large stream or pond; a 

 severe drought occurring over a fairly large area, prolonged suf- 

 ficiently to dry up all the water within that area, would cause all 

 the species represented in that year by apterous individuals only 

 to become extinct. 



In my outdoor observations on water-strider responses and 

 water-strider habitats, I have attempted to obtain some informa- 

 tion on the points to which I have directed attention, in connec- 

 tion with two different species, Gerris marginatus Say and Gerris 

 remigis Say. These observations have been recorded, mainly, in 

 the states of Illinois, Wisconsin, and New York. This work was 

 done in connection with the study of water-strider habitats of 

 varying and dynamic character, for example, rivers, creeks, 

 brooks, both permanent and intermittent, lakes, and ponds. While 

 all of these different kinds of habitats have contributed some- 

 thing to the general subject, the best data have been obtained 

 from the study of intermittent brooic habitats. X. 



On the surface of intermittent brooks, which frequently have 



/- a. rapid current, the two species of water-striders, Gerris remigis 

 and Gerris marginatus, are fairly common. The former specie^ >^ 



/ is found in greater abundance, as brooks of this character are 

 more nearly like its normal habitat. While individuals of the 

 latter species are few in number, as compared with those of 

 Gerris remigis, 3^et a considerable population may be found in 

 protected places where the force of the current is reduced, such 

 as sheltered bays, formed by tree roots and irregularities in the / 

 banks of the brooks, and in quiet backwaters. 



3 Loc. cit, pp. 109-110. 



