May, '03] ENTOMOLOGICAL NEWS. l6l 



being maintained. I do not mean that many imagoes are not destroyed, 

 but I do not believe that a comparison of the number of exuviae seen 

 with the number of imagoes seen gives us a correct idea of the number of 

 imagoes surviving. 



In Tennessee nymphs of Epiceschna heros were very abundant in a 

 ditch where I collected, but I never saw even a single imago. On the 

 other hand in adjoining swamps three species of Trainca were sporting 

 by hundreds as imagoes, and I found during an entire spring only one 

 exuvia. Tachopteryx thoreyi is known as a nymph by only the one speci- 

 men taken by Atkinson, though Graf has searched diligently for others, 

 but Graf, Atkinson and myself have taken numbers of imagoes. I am 

 afraid in the case of Neurocordulia obsoleta our ignorance is more re- 

 sponsible than the spiders for the few imagoes known. And I believe 

 the same is true of Ophiogomphus. 



In a carefully explored region, where observations have been made dur- 

 ing all seasons for a period of years, when the habits and requirements 

 of nymphal life necessitate a condition inconspicuous to us, and the habits 

 and requirements of imaginal life permit conditions not inconspicuous to 

 us, then our collections are filled with imagoes, while nymphs are rare ; 

 and in the same locality, but under exactly opposite conditions, we have 

 many nymphs and few imagoes. 



Then again, explained in the same terms, imagoes and nymphs of a 

 species may be common, or imagoes and nymphs may both be rare, 

 though I do not mean to say that all species are equally abundant or ap- 

 proximately so, and that we have only to discover the habitat of a rarity 

 to obtain it in numbers. Doubtless the new Somatochlora provocans is 

 rarer than some of the Libellulas, for example, but doubtless also, it is 

 relatively more abundant than the observations hitherto made would in- 

 dicate. E. B. WILLIAMSON, Bluffton, Indiana, Feb., 1903. 



While admitting the justness of Mr. Williamson's criticisms in a general 

 way, there are several facts to be pointed out which seem to support the 

 idea suggested, viz.: that spiders may be an important factor in diminish- 

 ing the numbers of dragonflies. Thus we also saw living spiders of the 

 same genus \_Dolomedes\ at other points on Lake Hopatcong, running 

 over the stones and the small wooden piers so common on the shores. 

 The significance of the boathouse observations is this : the shelter there 

 afforded protected the spiders' webs and exuviae, the remains and exuviae 

 of the dragonflies, from destruction by the weather and so preserved a 

 record of events similar to those which doubtless took place outside the 

 boathouse, but of which no trace remained at the time of our visit. I do 

 not deny that the causes cited by Mr. Williamson are also powerful 

 agents in decreasing the Odonata, but I venture to suggest that destruc- 

 tion by spiders is a factor whose importance deserves investigation. The 

 whole matter of the "vital statistics" of insects is one about which we 

 have few exact data. 



