BULLETIN 



OF THE 



BROOKLYN ENTOMOLOGICAL SOCIETY 

 Vol. XV February, 1920 No. i 



MIGRATORY RESPONSES OF WATER-STRIDERS DURING 

 SEVERE DROUGHTS.^ 



By C. F. Curtis Riley, The New York State College of Forestry 

 at Syracuse University, Syracuse, New York. 



It is well known that certain species of water-striders are poly- 

 morphic with respect to wing development. There are macrop- 

 terous, brachypterous, and apterous forms. Kirkaldy^ (p. 109) 



i- has observed six different variations^- in wing development, among 

 the brachypterous individuals of the species Gerris lacustris 

 Linne. These alary differences are pointed out here only because 

 of the modifying influence that they must exercise on the migra- 

 tory responses of the gerrids. Such variations in the develop- 

 ment of wings not only must act as modifiers of the manner of 

 migration, but they also must exert an influence with respect to 

 the number of individuals that migrate during different seasons. 

 / Attention is directed to the fact that the number of macropterous 



/ and apterous forms var)( from one season to another. 

 ' During periods of sustained and severe droughts the migration 



responses of both macropterous and apterous water-striders are 

 particularly interesting and worthy of observation. It is not only 

 of importance to obtain information concerning the modes of 

 migration, but it is also of consequence to discover what becomes 



1 For a more complete consideration of many points mentioned in this 

 paper, attention is directed to a recent publication by me : Riley, C. F. C, 



- " Some Habitat Responses of the Large Water-Strider, Gerris Remigis 

 /I Say," American NaturalistT*" Vol. LIII (1919), pp. 394-414, 483-505; Vol. 

 LIV (1920), pp. 68-83. 



2 Kirkaldy, G. W., " A Guide to the Study of British Waterbugs 

 (Aquatic Rhynchota)," Entomologist, Vol. XXXII (1899), PP- 108-115. 



1 



.;;v\W»«Va»'T 



