Rhithrogena germanica

Rhithrogena germanica is a European species of mayfly, and is "probably the most famous of all British mayflies", because of its use in fly fishing. It is known in the British Isles as the March brown mayfly, a name which is used in the United States for a different species, Rhithrogena morrisoni. It emerges as a subimago at the end of winter, and can be distinguished from similar species by a dark spot on the femur of each leg.