Probably more familiar in Western US waters, the Ida May is a Green Drake type imitation of the Mayfly family. Hatching every two years they are usually burrowed into the sandy bottoms of streams and they are the largest of the Mayfly species in southern Appalachia.
I have heard, yet never experienced, these hatches up around Beaver Dam Creek in far eastern Tennessee not far from where the Appalachian trail crosses the main roadway. Regardless, it's a great buggy type bug and should be in your fly box.
Fished typically in the spring to early summer. Sizes #14 to #16 are your best bet given these are very large bugs.