stone fly

GNU Webster's 1913

1. n. (Zoöl.) any one of many species of pseudoneuropterous insects of the genus Perla and allied genera; a perlid. They are often used by anglers for bait. The larvæ are aquatic.

WordNet 3.0

1. n. primitive winged insect with a flattened body; used as bait by fishermen; aquatic gilled larvae are carnivorous and live beneath stones