The Thomas Yellow Mayfly is one of our premium Mayfly patterms. The Mayfly is one of the most anticipated hatches of flies in the fly fishing calendar. At the end of May and early June these large upwing flies will emerge on rivers and still waters through out the UK. Often ignored by fish for the first day or two, once the fish switch on to the mayfly as food then they can loose all caution and rise freely to eat these large insects. Once the fish are feeding then fishing a dry mayfly pattern can be extremely successful and very exciting.