The stonefly, Nemoura cinerea, by possessing two pairs of wings indicates they are not true flies (Order Diptera); they are placed in the Order Plecoptera, meaning ‘braided wings’, which refers to the ornate venation of the wings.
They can be found either flying slowly and erratically over stony streams and rivers, or crawling amongst the stones and vegetation along the waterside where the males can communicate with females by knocking their abdomen on the substrate to produce a specific rhythm of pulses.
The fertilised female flies over the stream and simply drops her eggs, coated with a sticky substance, into the fast-running water where they will adhere to stones to prevent them being carried away by the flow. The eggs hatch into nymphs (looking like miniature adults, but without wings) which, requiring well oxygenated water, and being sensitive to water pollution, are important indicators of water quality.
The nymphs live amongst the stones feeding on submerged leaves, moss, and other detritus. They pass through many moults over several years before leaving the water, attaching themselves to a stone or the like, and undergoing a final moult before emerging as an adult.