March Brown mayflies are a species of mayfly that typically emerge in late winter or early spring, usually in the month of March. They are widely distributed across Europe and North America and are often found in cold, clear streams and rivers. Adult March Brown mayflies are characterized by their reddish-brown bodies, large wings, and prominent antennae. They typically mate and lay eggs in the same location where they hatched, before dying off within a few days. March Brown mayflies are important to aquatic ecosystems as a food source for fish and other aquatic organisms, and their emergence can trigger productive feeding activity in fish, making them a popular target for fly anglers.