Isonychus

Isonychus is a genus of mayflies belonging to the family Isonychiidae. These mayflies are found in North America and parts of Asia. They are known for their streamlined body shape and strong swimming abilities, which allow them to thrive in fast-flowing rivers and streams.

Isonychus nymphs are predaceous, feeding on other aquatic insects and small invertebrates. They possess elongated bodies and legs adapted for clinging to rocks and other submerged surfaces in turbulent water. They also have prominent gills that are used for respiration in the oxygen-rich environment of their habitat.

The adults, like all mayflies, are short-lived, often surviving only a day or two. Their primary purpose is reproduction. They emerge from the water, mate, and the females then lay their eggs in the water, completing the life cycle.

Anglers often imitate Isonychus mayflies in their artificial flies because they are a significant food source for trout and other fish in streams where they occur. The relatively large size of the nymphs and adults makes them an attractive target for fish, and fly fishing patterns that closely resemble Isonychus species are often successful.