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THE AMERICAN NATURALIST [Vol. LlII 



Maiikato, ^liiniosota, a few hundred yards from a larg-e 

 swamp, near tlie confine? of the oity, T observed them for 

 several ni^-hts, as they flew in great swarms, around the 

 globes of the street arc lights. On the ground, within a 

 radius of thirty to fifty feet of certain of the lights, were 

 thousands of these aquatic bugs, both alive and dead. On 

 several occasions, it was possible, in thirty minutes of 

 time, to fill a half bushel measniv with the insects. In 

 the fall of 11)15, at Milwaukee, Wi^con.i n. in ih.- \icinily 

 of Lake Park, between the JMilwankt-e [I'ww and tlu' w.-^t 

 shore of Lake Michigan, T o])served >evernl occurrences 

 similai" to those just described. In these instances, the 

 a(iuatic bugs wei'e not present in quite such large num- 

 ])ers as in the former cases. The point of importance 

 here is, of course, the fact that members of the two 

 groups, Benacus and Belostoma, respond positively to 

 light during migration. Comstock and Comstock (1895, 

 p. l.'^S) refer to somewhat similar responses. All these 

 facts add still more emphasis to the probability that 

 alate gerrids. when migrating, locate streams and stand- 

 ing water ])y means of vision. It should be recalled that 

 such hodic- of watei' are effective reflecting surfaces. 

 ]|()\vc\ cr. it i> <|ultc possible that both alate and apterous 

 indi\-idiiai- <>> ///s nuirff'nxbtus are res])onsive to mois- 

 tniv at ui-catcr (li^tanccs than i- the ca-e with apterous 

 inei.iher^ of r;. ><n>u,^^. jftlii. -.ImnM prove to be 

 the ca^e, it wouM W .,f .-i-^l^Pi! cc il,.. ucn j.l^ in find- 

 ing l)()die> of water. Fnrtiier, it nniM l)c i-ecalh'd that the 

 ])ond to which AVei-> directs attention covered an area of 

 8,000 square feet, wliile the pools of water to which I refer 



Ft is i>robably true that many artlii-otiods resi)0]id 

 ivadilx to moisture. But there i^"n<.t ;i a1 dea! of ex- 

 pei-imciilal evidence recorded in the literature, tieatluu' 

 of tiM' hehavior of memliers of the lii'oup. that pi-e-eiits 



the Mibjcct under di^cu^^lon. ' tL 'e\|!'Vim^^^ 



