164 THE CA.NAWA.N ENTOMOLOGIST. 



PRELIMINARY STUDIES OF N. AMERICAN GOMPHIN.^. 



BY JAMES G. NEEDHAM, CORNELL UNIVERSITY, ITHACA, N. Y. 



Examples of the emphasized importance of larval life better than 

 that furnished by the subfamily Gomphinae of Odonata are few even 

 among insects. The nymphs live under the sediment (mostly organic 

 debris) which falls to the bottom of ponds and streams. They are 

 aquatic burrowers which live at such slight depth that their anal 

 respiratory orifice is never beyond the reach of clean water. This thin 

 stratum, which forms their home and which they only leave to trans- 

 forhi, is one of great biologic richness. In it they have found room 

 for development in enormous numbers and necessity for extreme 

 specialization. T'hey are, at least when well-grown, among the more 

 powerful members of its teeming hidden population. The imagoes 

 emerge, flit about under cover for a few days, lay their eggs and die. 

 They emerge largely by daylight and are subject to great decimation 

 of numbers at this time, and are sought later by numerous powerful 

 enemies. The females which live to oviposit lay a very large number 

 of eggs. A female of GompJiiis fraternus laid for me in a watch glass 

 of water over 5,000 at one time. The imagoes of the ancient genus 

 Gomphus are regarded as a race of weaklings. Their nymphs, on the 

 contrary, are splendidly equipped for the battle of life. And it is to the 

 perfection of their adaptation that the prevalence of Gomphines with 

 us is due. 



These conditions have developed a large and very uniform series 

 of imagoes, with one colour pattern, one plan of venation, one habitus, 

 consisting of many very closely related species difticult to study. 

 Specific characters, though slight, are yet constant. The slight specific 

 variations of an ancient colour pattern long retained are unusually 

 reliable. Secondary sexual characters reach here their maximum of 

 importance and of specific individuality. This is as one would expect, 

 recalling the vicissitudes of adult life and that its chief concern is with 

 reproduction. 



The real competition of life, however, is carried on by the nymphs, 

 and the outcome of it is that they have become specialized. They 

 have developed along several lines and have become segregated into 

 vy?ll-niarHed natural groups which are not so obvious among the imagoes, 



