Stone flies are a diverse family of insects that are adapted to well oxygenated streams and rivers and cannot survive in polluted water. Stone fly nymphs have fixed gills that can only extract oxygen in clean moving water. If trapped in still stagnant water, they die quickly. Most stone flies crawl out of the water to hatch, usually on rocks or shrubbery. The normal procedure is for stone fly nymphs to migrate to shore to hatch. This activity is attractive to trout and salmonids. Some smaller species will hatch in the middle of the river at the water's surface much like mayflies. Nymphs like giant stone flies live in the rivers for as long as three years before they hatch into winged adults. They are attractive to trout in several sizes, almost year round.
As the stone fly nymphs grow they must take over a larger territory. The redistribution of these territories usually happens in masses with many aquatic insects changing territory at the same time. This is called a behavioral drift and commonly happens immediately after sundown. The largest behavioral drifts of most stone fly nymphs occur September through May. These mass drifts (or shifts) of insects occur during the twilight hour of the morning and late evening. During these periods stone fly nymphs are moving down stream. Many are caught in the currents and swept downstream out of control. Trout target on these vulnerable treats and will feast until gorged. You need to carry patterns in many different weights to cover different water speeds and depths. The flies we have available will cover all of the subsurface "giant stone fly" nymph activity. There are also patterns such as the Little Golden Stone and the Bead Head Rubber Leg Hare's Ear that will cover many smaller species as well.
Several weeks before the hatch, salmon flies and golden stones will start to migrate to staging areas along the banks. No other occurrence in our rivers and streams will produce a feeding frenzy like the migration of big stone fly nymphs. Even the largest trout find it impossible to refuse a big stone fly nymph fished deep along the bottom. The peak of this activity is the last two weeks before the hatch and we have been fishing these hatches for over 40 years. If you want an amazing day or 10 on the water with thousands of trout feeding in a mass frenzy, then stock up on the flies you'll find in our May Flies and Stones Directory