Juvenile stoneflies are called ‘nymphs’. Stonefly nymphs nearly always live in rivers and streams, as they require flowing water to breathe. Most are considered ‘crawlers’, living on and under rocks or other substrates on the stream bed. Different species feed on a variety of food items, including algae, detritus, or other invertebrates. Most species emerge after only one year, though large-bodied species tend to live for multiple years before emerging as adults. Unlike most mayflies or caddisflies, stoneflies typically emerge by crawling onto the bank, where they molt into the winged adult.

Identifying juvenile stonefly nymphs is quite easy. All stonefly nymphs have two claws and two tails. They also have three distinct thoracic segments.

Stoneflies are considered to be the most sensitive group of aquatic insect to environmental disturbance, and their presence in streams is indicative of a healthy ecosystem.