Stonefly Mating and Reproduction
The male signals his desire to mate to the female by beating the ground with the tip of his abdomen. The pattern of beats is different for each species. If the female is receptive she replies with a series of taps on the ground with her abdomen. The pattern of taps is different in males and females, and between different species.
Mating usually happens on the ground or on vegetation. The female then flies over the water dipping her abdomen in to wash off the eggs, or she swims on the surface while laying eggs. Each female can lay hundreds of eggs.
The eggs have a gelatinous coating that swells up and absorbs moisture. This enables some eggs to survive in streams that dry up periodically.
In the U. K. most species have one generation per year. The eggs stage lasts about a month. Cold can halt the development of the nymph, and then a generation may take more than one year to complete.
Nymphs are usually found on stones on stream beds, and are an important food item in the diets of many fish caught by fly fishermen. They are poor swimmers though. They look similar to the adult (see below), but are wingless. They get most of their oxygen by diffusion over the body surface, but some species also have gills. They are mainly vegetarian, eating moss and algae, and detritus but some larger nymphs will eat the nymphs and larvae of other aquatic insects.
Development from egg to adult can take 1 - 3 years, and during this time the nymph can moult as many as 33 times. In winter the nymphs hide in the mud.