Tricos are a small mayfly that can hatch in such prolific numbers they can blanket the water. This is a long hatch, often hatching from July into October depending on the watershed. The duns can be a pale gray/olive in color to almost black with light gray wings. The hatch is either in late evening or early morning. Given the numbers and size of the hatch, this is an important food source for trout. While small, size 20-24, the fishing can be fantastic as trout will lose their normal cautious behavior and lazily sip the surface. This can be characterized in the late evening with a smacking sound where the trout are cruising the surface gulping spinners.