EMERGENCE OF A MAYFLY FROM ITS 

 NYMPHAL SKIN.* 



F. H. KRECKER 

 Department of Zoology and Entomology, Ohio State University 



The emergence of a subimago mayfly from its nymphal 

 skin observed by Superintendent George F. Miller and Captain 

 Bickford, both of the Ohio State Fish Hatchery at Put-in-Bay, 

 Ohio, and later described to me by them, impressed me as 

 being of sufficient interest to warrant the addition of one more 

 account to the number that have already been published 

 regarding the subject of mayfly emergence. 



The transformation occurred in a large, portable fish tank 

 which had been standing for a number of weeks on the dock 

 in front of the Hatchery building. This tank had been filled 

 with water from the lake by means of a steam pump which 

 had its intake lying very near the bottom and, presumably, 

 the mayfly nymph had been drawn up with the water. Mr. 

 Miller and Captain Bickford were standing at the side of the 

 tank and were thus in an unusually fortunate position for 

 observing the entire process of emergence. It occurred some- 

 time during the month of June. The nymph swam upward 

 from the bottom of the tank and when it reached a point about 

 six inches beneath the surface of the water the nymphal skin 

 split along its dorsal surface and the subimago began to push 

 out. By the time it had reached the surface the subimago had 

 freed itself entirely from the nymphal skin and was able to 

 fly away immediately. 



Neither of the men was familiar with the names of ephemerid 

 species or the criteria for distinguishing them and therefore 

 it is impossible to say to which one this individual belonged. 

 The species which occur most commonly in the region of 

 Put-in-Bay during the late spring and early summer are 

 Hexagenia bilineata and Ephemera simulans. 



Needham ('18) describes the emergence of Hexagenia 

 bilineata as follows: "Transformation occurs at the surface 



Papers from the Lake Laboratory, Ohio State University, No. 74. 



155 



