Siphloplecton basale is usually referred to as the Gray Drake. This is ther first really big mayfly to hatch in the northern Wisconsin freestone streams and rivers. That is the good news. The bad news it the Gray Drake is a sparse hatch and has little importance to fly fishermen.
The Gray Drake crawls out of the water to molt into a dun. You will often see one fluttering around the streams in April around the time the Hendrickson hatch. There really are not enough of them to be of any real importance. But seeing a big gray mayfly, size #8, in the air does get the blood pumping with the hopes some big trout will be on the look out for these bugs.