Stone Flies (Plecoptera)
Stone flies are primitive insects, fossils show that they have existed for 220 million years; Stone flies generally represent a much smaller percentage of the trout's diet than do May flies and caddis flies. This type of generality can be quite misleading however, forever if stone flies represented less than 10 percent of the trout's diet on a particular stream, it is quite possible to arrive on the that stream for several days of fishing only to find that prolific stone fly emergences or oviposting flights are in progress, causing trout to feed selectively. It may be the only significant stone fly activity of the year on that particular stream, yet if the angler were unprepared he would probably have a very unsuccessful fishing trip. Hence, serious fly fishermen should make every effort to learn about this interesting order of insects and the effect they have on trout.
The size range of stone flies is extreme; some tiny Capnia species may be only 4 to 5 millimeters in length, while the legendary pteronarcys flies approach 50 mm (2 inches) in length. Generally, the life cycle of the smaller stone flies is one year, while maturity may take two or three years for the large Pteronarcys and Acroneuria stone flies.
The combination of seasonal succession, feeding habits, and habitat preferences reduces the competition among the species of the stone fly and species of other orders. For example, the tiny Capnia and Taeniopteryx stone fly nymphs spend spring and summer in the substrate as tiny mummy like (depausing) nymphs. They resume feeding on algae and detritus from September to late winter or early spring. Many hatch through the winter and early spring, although April hatches are the best known to fly fishermen. We have fond memories of early April Teniopteryx activity on the gentle Brodhead's in Pennsylvania. The nymph imitations and flush floating emerger patterns did well when the activity didn't clash with the prolific early season Beats may fly, which emerge in similar water temperature rages 42 – 52 degrees Fahrenheit.
There are six stone fly families in North America; three are herbivorous (vegetarians_ and are of the Frilipalpa group; three are carnivorous or omnivorous and belong to the Selipalpia group. The herbivorous group includes pteronarcidae, Peltoperlidae, and Neoruidae families, most of which feed on value green algae, diatoms, and plant matter. The pteronarcidae family includes the giant stone flies of pteronarcys genus. Ptervonarcys californica is called the salmon fly by western anglers and is responsible for legendary hatches on such rocky mountain rivers as the Yellowstone, Madison, and Big Hole. Pteronarcys dorsata is the eastern and Midwestern equivalent of the genus, but the hatches are not nearly as significant.
The Neoruidae family includes the tiny winterish and early spring hatching stone flies of the Capnia subfamily Capuiidae_ and Taeniopteryx genera subfamily Taeniopteryginae). And early black stone fly (Capnia), given to these flies for their early emergence.
The carnivorous or omnivorous stone flies are the Perlodidae, Chlorperidae, and Perlidae families; the latter are true carnivores. The perlodidae and chlorperidae stone flies are omnivorous and many species of the latter are considered herbivorous. The Acroneuria nymphs (family perlidae, subfamily Acroneurinae) are the most aggressive carnivores.
They are prolific on the larger stretches of our best eastern need Midwestern trout rivers. They are flattened in cross section and their color patterns are strikingly contrasting and reliable for identification. The plant eating families are usually round in cross section and concolorous.
Most stone flies crawl out of the water on rocks or other objects before they emerge as adults. Thus the act of emergence generally sets up few feeding opportunities for the trout. A few species may hatch on the surface, especially if the stream lacks boulders or other convenient emergence objects. The best opportunities, as far as the trout are concerned, occur during surface activity or when the nymphs are migrating to their emergence sites. The adults are quick afoot and do very little flying once they reach the shore. Mating takes place not in the air but on the ground or on plants.
As with the caddis, many species, many species of stone flies feed in the winged stage. The filipalpa stone flies are known vegetation feeders, while the Selipalpia adult stone flies (carnivores) have insufficient mouth parts and do not feed. The large vegetarian Pteronarcys stone flies are an exception and do not feed in the adult stage.
Ovipositing is performed in various ways. Many species crawl to the water's edge to deposit their eggs uneventfully. Many species of Taeniopteryxl, Capnia, and Allocopnia alight on the water to release their eggs. This presents better opportunities for the trout when the insects are in sufficient numbers. Other spring and summer forms, such as the large Pteronarcidae and Perlidae families, drop eggs en masse from the air.
Over the years, we have found the large stone fly nymph imitations to be the best producers during periods of inactivity. Imitations of the Acroneuria group are especially effective, since these carnivores crawl from the crevices more often than other groups while hunting for food or migrating to other areas. Pteronarcys imitations may do better on western rivers or on the head waters of eastern trout rivers where Acroneuria nymphs are scarce. Although these larger nymphs are not available in numbers sufficient to cause selective feeding, they may be to the trout the most appealing subsurface food during periods of inactivity. Thus it is understandable why the large stone fly nymphs such as the Golden Stone, Catskill Coiler, Montana, Bitch Creek, and Stone fly Creeper, in sizes 4 thru 10, are the top choice of the most self confessed nymphers.
“Masters on the Nymph”
By Caucci and Nastasi
http://www.seattlegrapevine.com
