I was fishing in west central Indiana on July 18. I was hit with a mid morning hatch of some size 18 or smaller three tailed gray mayflies. It was about 9:00A.M. Does anybody know what these might be?I will post pictures later from my cell. I'm not sure how good the pictures will be though. Thanks.
The possibility that Louis suggests is a good one. At this time of year, (small, grayish) three-tailed mayfly duns that emerge around mid-morning could very well be Paraleptophlebia species, aka Summer Blue Quills. Another possibility might be one of the little ephemerellids of Serratella. Dry flies tied to imitate the duns of either genus would be basically the same.