This was a soggy exoskeleton floating in the lake when I picked it up. Once dried out, it looked a whole lot better, though it's still pretty papery and fragile. I believed this to be an exoskeleton from one of our mayflies (which don't only come out in May), but have since found out that the 2 pronged 'tail' distinguishes it more specifically as a stonefly instead. (Mayfly naiads generally have 3 prongs). Stoneflies are intolerant of water pollution, so can be a good indicator of water quality.