1911] May-Flies of Fall Creek, N. Y. 99 



Potamanthus sp. 



Only two partly grown nymphs of this form were found. 

 Both were taken on June 29 in sandy mud washed by a gentle 

 current. 



Hexagenia variabilis Eaton. 



Full grown nymphs of Hexagenia variabilis Eaton the 

 largest of our burrowing May-flies, were found abundantly 

 on the sunny afternoon of May 16 in company with Ephe- 

 merella and the large dragon-fly Cordulegaster. At the 

 place where they were Fall Creek is a leisurely brook 

 meandering through sparse woodland and open meadow, 

 and hemmed in by soft muck banks. In one such area 

 the sloping banks were mined by Hexagenia nymphs, the 

 open burrows showing only two or three inches apart. 

 Most of the burrows were apparent by their round open- 

 ings, but from some hairy caudal setae protruded at full 

 length. When a nymph was pulled out it speedily began to 

 burrow again, placing the forelegs together with the blade-like 

 tarsi held vertically. It next pressed them forward and outward 

 at the same time wedging the head between them in the cavity 

 thus made. This movement was followed by a sudden lurch 

 of the body forward accompanied by wriggling of the abdomen. 

 During these motions the second pair of legs was folded close 

 up to the body, while the third pair was held outstretched 

 ready to brace against the mud. These motions rapidly 

 repeated enabled the nymph to bury itself in a surprisingly 

 short time. Some of the soft ooze taken from where the bur- 

 rows were most numerous was later examined in the laboratory 

 and found to be packed with diatoms. Stomachs of two of the 

 nymphs were found full of silt and diatoms showing that the 

 nymphs had found plentiful forage as they burrowed. Between 

 two and five o'clock of this afternoon about twenty-five sub- 

 imagoes emerged within a few yards distance. They flew up 

 slowly and usually settled on low shrubs. Many were cap- 

 tured on near-by alders two to five feet from the ground where 

 the yellow markings on their bodies and wings made them 

 conspicuous. 



