In the Western states, stoneflies are held in high esteem as anglers anxiously anticipate them for their large numbers and size (Video). Generally, stoneflies are the largest of all insects that live in the water.
Like many insects, stoneflies have a successful lifecycle that dates back over 250 million years to the Permian Period and not much about them has changed.
Stoneflies have the characteristic six legs of insects, but four wings that are folded flat on top of the abdomen. Coloration is black, brown, yellow and tan. Despite 200 million years of evolution, they are considered awkward fliers.
Some general lifecycle traits of all species start with the females depositing hundreds of tiny eggs over a stream that quickly find their way to the bottom among the rocks. Nymphs then grow and molt 12-36 times before leaving the water. Some species can require up to three years before they mature into adults. As nymphs, they can be found under rocks feeding on algae, mosses and even other aquatic invertebrates.
While Mayflies and caddis flies emerge out of the water, most stoneflies hatch from the shoreline. Each species varies, but stoneflies will swim to the banks and crawl out of the water onto rocks or plants to molt into winged adult insects. Stoneflies are regarded as more nocturnal and you will more likely see the molted shucks and not see the actual emergence. Another difference between Mayflies and Stoneflies is that many species will have mouths and can feed during the weeks they live as adults before finally mating and dying.
Seeing active stoneflies and shucks is a good sign to start fishing with a stonefly nymph or a stimulator dry fly.
To learn and discuss more mayflies on the site head over to the Hatch and Entomology Forum. Beginners can follow along and learn more in the Beginners Forum.
A great online site to follow and get deep into the Latin is Troutnut and his Aquatic Insects of our Trout Streams. A must-read!! BugGuide has more details as well.