5 GEORGE V. SESSIONAL PAPER No. 39b A. 1915 



V. 



LIFE-HISTORIES OF GEORGIAN BAY EPHEMERIDAE OF 

 THE GENUS HEPTAGENIA. 



By W. A. Clemens, B.A., University of Toronto. 



(Plates XV — XVIII, and 1 figure in the text) 



In the preceding paper on the mayflies or Ephemeridae of Georgian Bay, the 

 consideration of the genus Heptagenia was omitted for reasons there stated. The 

 present paper is based on the results of observations and breeding experiments 

 in connection with this genus covering a period of slightly over three months 

 during the summer of 1912. 



The genus Heptagenia is a comparatively large one as it occurs in America. 

 Rev. A. E. Eaton in his Monograph of Recent Ephemeridce made a summary of 

 the then known North American species, amounting in all to at least 13, some of 

 them, however, having been referred tentatively to the genus Ecdyurus. In 1910 

 Mr. Nathan Banks described 4 new species, making a total of 17 species recorded 

 from America. Up to the present the nymphs of only 2 of these have been described 

 namely. Heptagenia pulchella Walsh, and H. interpunctata, Say, both by Professor 

 J. G. Needham in 1901 and 1904 respectively. In this paper are given the descrip- 

 tions of the nymphs of five more as well as descriptions of the nymph and images 

 of 3 new species.* 



The nymphs of this genus inhabit swift water for the most part ; clinging 

 close to the sides and bottoms of stones. They are adapted to this life by reason 

 of many interesting specializations, chief of which are, much-flattened bodies, 

 flaring margins to head, spreading legs with flattened femora, pectinated claws, 

 gills dorsally placed in an overlapping series and spreading setae. A few species, 

 however, are common in quiet water, notably Heptagenia canadensis, and H. 

 frontalis while H. tripunctata was found to be everywhere abundant. The 

 nymphs are quite active, for when a stone is lifted from the water they scurry 

 over its surface usually seeking the lower side. The clinging habit was frequently 

 demonstrated when quite a number were brought in and put in a vessel of water 

 without a stone or stick for them to cling to; not having anything else, they 

 would begin clinging to each other and soon would all be in a single mass. As 

 for food, being herbivors, they usually find abundance of various algal forms 

 on the stones to which they cling. 



A Heptagenia completes its life-cycle in a year. The egg is deposited in the 

 water and hatches in about 40 days. The remainder of the mayfly's life is spent 

 in the water as a nymph with the exception of a short aerial life of from 2 to 4 

 days as a subimago and imago. As the time of emergence approaches, the nymphs 

 probably migrate to the quieter water. I have not observed a Heptagenia emerge 



*Since the above was written thesa new species have been describzd by the writer 

 (Clemens) '13). 



396—9 II 



