Ephemerellidae, known worldwide as Blue Winged Olive, are considered the most difficult to imitate ephemeral, for their extreme variation in colors from river and river, but especially because it is a genus very sensitive to changing environmental conditions, so we almost always see a variability in the behavior of both insects and fish in their regard. Fly-fishers know that they are obliged to have a high number of imitations in terms of colour, size and vital stage of reference of the insect.