any of an order (Plecoptera) of soft-bodied, winged insects whose nymphs live under stones in swift streams: often used as bait in fishing
See stonefly in American Heritage Dictionary 4
stone·fly
noun
Any of numerous weak-flying insects of the order Plecoptera, whose flat, elongated nymphs live under stones along the banks of streams. Adult and larval stoneflies are used as fishing bait. Also called plecopteran.