THE CANADIAN ENTOMOLOGIST 409 



THE KNOWN NYMPHS OF THE NORTH AMERICAN 

 SPECIES OF SYMPETRU-M (ODONATA). 



BY E. M. WALKER, TORONTO. 



Of the eleven North American species of Sympetrum, generally 

 recognized, the nymphs of all but two have been reared or de- 

 termined with practical certainty. These two are S. ambi^jium 

 (Ramb.) and 5. niadidum (Hag.). Of the nine others I have ex- 

 amined nymphs of all except 5. corriiptum (Hag.) and S. illotum , 

 (Hag.). These, how^ever, have been sufficiently described and 

 figured by Needham^ to make possible their inclusion in the key 

 given below. 



In addition to material collected by myself I have examined 

 a considerable number of specimens kindly lent me by Prof. Need- 

 ham, and also an exuvia of S. scoticum Donov., with the imago 

 which emerged from it, found at Red Deer, Alta., by Mr. F. C. 

 A\ hiiehouse, who kindly gave the specimens to me. 



The study of these Sympetrum nymphs has been unusually 

 difficult, and the results are far from satisfactory. Variation 

 within the limits of the species is generally so great that it is seem- 

 ingly impossible, in most cases, to find any constant character 

 by which a particular species may be recognized with certainty. 

 For this reason the key which is given here must be used with a 

 great deal of caution. 



I have not included in the key the form which I consider to 

 be typical S. riibic undid iim, as I have not reared it nor seen nymphs 

 which I could safely assign to this race. I have, however, several 

 specimens of the nymph of 5'. rubiciindidiim decisum (Hag.) from 

 Prince Albert, Sask., but they differ from Needham's description 

 of rnbicundtdum^ in the extreme reduction of the dorsal hooks 

 and are readily separated from my nymphs of obtrnsiim. Needham 

 reared both of these species and found no differences between 

 them. This matter will be more fully discussed, later. 



The nymph of Sympetrum may be characterized as follows: 

 Head rather large, the width across the eyes being little less than 

 that of the abdomen, not more than twice as broad as long; eyes 



l~Bull. 68, N. Y. State Mus.. 1903, pp. 271-273, No. 16, 17;BuIL 47, N.' Y. 

 Slate Mus., 1901, pi. 2.5, fig. 1. 



2 Bull. 47, N. Y. State Mus., 1901, p. 525. 

 December, 1917 



