The large stoneflies of the family Perlidae provide “golden” opportunities for the fly fisher across the entire continent.

A hundred and fifty years ago the California gold rush sent tens of thousands of strike-it-rich dreamers to the streams and rivers of the Sierras and intermountain west. But what you might not realize is that this rush for gold is still happening today. Every year, as the seasons shift from spring to summer, strike-it-rich dreamers with fly rods, rather than pick axes, in their hands head to the rivers and streams throughout the west in search of the fly fisher’s equivalent of the mother lode – the annual hatch of golden stones (Hesperoperla pacifica & Calineuria californica). In terms of wild and exciting fishing this annual event is truly a gold mine. During the peak of a good hatch bank side vegetation literally droops from the weight of fat two-inch golden colored stonefly adults, and trout stomachs bulge like overstuffed bratwursts. But such abundance is not limited to just western trout streams. Midwest and eastern trout streams have their own golden stone counterparts though they go by more localized names like elegant stone, common stone, central stone, and enigmatic stone. One thing all these species have in common is that they are members of the stonefly family Perlidae.

Perlidae is an eminently successful family of stoneflies. In North America the family contains 15 genera and 48 species, with a distribution that spans from the Pacific to the Atlantic and from Mexico to the arctic. With such diversity generalizations about color, size, hatch dates, and best fly patterns are problematic at best. Still a few things can be said that apply to the family as a whole.

The nymphs of perlids can be recognized rather quickly by the thickly branched clump of filamentous gills attached near the base of each leg. About half the species also have a set of branched gills at the tip of the abdomen between their tails. Coloration of nymphs within the family varies considerably, but nearly all species show distinct dark and light color patterns on the upper surface of their thorax and head. Overall body colors range from black or dark brown to golden brown or light tan. The size of mature nymphs varies between species from a half inch to one and a quarter inches long. The majority of species tend to the large end of this range and the family in general is one of large insects.

Identifying adult perlids from other adult stoneflies requires a bit more careful examination than required of the nymphs. For species that are over an inch long, their size is the first good tip. Like the nymphs they can range from a half-inch to one and a quarter inches long. Adults are rather uniform in color without the dramatic color patterns common to the nymphs. Adult colors range from light tan to almost white underneath, to golden brown or almost black on top. The common name “golden stone” refers to the golden brown color of the two most important species in western streams – Hesperoperla pacifica and Calineuria californica. Finally, at the base of each leg a small clump-like stub remains where the gills of the nymph once where. These remnants of the nymphal gills are perhaps the most definitive characteristic for recognizing adults of this family. Seeing these gill remnants, however, does require a close look, and while they are visible with the naked eye a small hand lens will help you see them.

Like all stoneflies perlids are sensitive to pollution and require good water quality to thrive. Plenty of dissolved oxygen is a must, and therefore streams with cold, well oxygenated water produce the best populations of large stoneflies like perlids. The best place to find such conditions are in mountainous areas. This is one reason why the West, with its large number of mountain streams fed by cold snow melt through the summer, have such prolific hatches of stoneflies. The Mid-west and East have fewer streams that meet ideal conditions for stoneflies. Mountainous areas like the Ozarks and Appalachians have good populations as do some spring creeks that maintain cold water temperatures through the summer months. Any stream will see a decline in stonefly numbers if water quality is degraded, which is the main reason stonefly hatches in many areas have declined from historical levels. Fortunately trout have many of the same water quality requirements as stoneflies. Therefore, a stream with a healthy trout population probably has water quality conditions suitable for all but the most sensitive stoneflies.

When it comes to behavior, nymphs of this family stand out as some of the fiercest predators of all aquatic insects. They mostly prey on smaller aquatic insects with small Diptera larvae like chironomids, mayfly nymphs and caddisfly nymphs topping their list of preferred happy meals. Some very fascinating predator-prey studies have been done with these stoneflies. For example, it has been shown that some Baetis mayfly nymphs can “smell” the presence of a large perlid stonefly nearby and quickly flee the area. The presence of non-predatory stoneflies causes no such response. Another example of their predatory nature often occurs when I teach streamside entomology classes. We generally put samples of insects from the stream in white water filled trays for a better view. This little self-contained insect zoo often includes some large golden stone nymphs. The tray is like a zoo without cages to separate predators from prey, and it usually doesn’t take long before one of the big golden stone nymphs begins to eat one of the small mayflies or caddisflies. It leaves quite an impression on those watching – a bit like seeing a cat catch a mouse – and clearly shows just how predatory these nymphs can be.

The need for oxygen and small insects to eat causes most perlid species to live in riffle areas of streams and rivers with a rocky, cobble bottom. The water splashing over the rocky bottom creates turbulence that oxygenates the water. In addition riffles are home to a wide variety of small insects for the perlids to eat. To satisfy their hunger these large nymphs stay constantly on the move, crawling over the boulders and rocks on the stream bottom in search of their next meal. This also means they are susceptible to getting washed off the bottom into the current where hungry trout quickly turn predator into prey. As a result nymph patterns that imitate the dominant perlid nymphs in the stream you are fishing can produce excellent results.

Most perlid species require two years to complete nymphal growth before emerging into adults. The same species living in colder water at higher elevations or further north, may require three years to reach maturity. In either case, this multi-year life cycle means that there will be a wide range of sizes of nymphs in the water at any one time, and the nymphs of younger year classes will still be present and available to fish even after the emergence of adults has occurred. This increases the overall importance of imitating the nymphs. In addition stonefly nymphs crawl out of the water to emerge into adults. As a result a week or two before adult emergence begins mature nymphs begin migrating from mid channel areas to areas along the shore. These migrations produce a large increase in the number of drifting nymphs, and is the ideal time to fish nymph imitations. But like many hatches, it’s the adults that create the most excitement for anglers. When adults are abundant dry fly fishing can be extremely exciting and productive.

Exactly when adults will be available on your local water will vary with where you live and weather conditions. For example, the golden stone hatch in Northern California typically occurs from early to mid May, while in Colorado it may not start until mid July and peak in early August. Adult emergence of Midwest and eastern species tends to occur in June and July. Cold spring weather will push the hatch a week or two later, while warm spring weather will result in an earlier hatch. Water temperature appears to be the main trigger for starting adult emergence. For western species adult emergence begins when water temperatures reach 50 to 55 degrees. Because stream temperature warms from downstream to upstream through the season, hatches start at low elevations and progressively move upstream. This phenomenon allows anglers to move upstream with the hatch and keep fishing where dry fly action is at its best for several weeks.

Adults emerge above the water, where the nymphs have crawled up tree trunks, rocks, or even bridge abutments, and are not initially available to trout. Dry fly action doesn’t start until they have mated and females begin returning to the water to lay their eggs. Mating occurs on streamside foliage a few days after emergence. Males have a unique method of attracting mates. A hard plate on the underside of the tip of their abdomen, called the hammer, is “drummed” against a branch creating just the right vibrations to attract a female – perhaps insects and humans aren’t so different after all. A few days after mating females begin flying back over the water to lay their eggs. Eggs are either released on the surface of the water or a few feet above the water. In either case many of the adults end up on the surface where flapping wings and thrashing legs create quite a disturbance. There is hardly a trout in the stream that can resist such large struggling prey and the dry fly fishing is on. It should be noted, however, that there is a difference in adult activity between western and Midwest and eastern species. According to Dr. Stan Szczytko, a stonefly specialist and professor of limnology at the University of Wisconsin, Midwest and eastern species of perlids rarely produce the same concentration of adults found on western streams. He feels this is probably due to an overall lower abundance of perlid stoneflies in Midwest and eastern streams because of more limited prime habitat – fewer coldwater mountain type streams, and a longer history of stream pollution problems than in the west. Because adult numbers are lower, the wild surface feeding activity, common during western hatches, is not so common for Midwest or eastern hatches. Dr. Szczytko did point out that even though surface activity may be less predictable, nymph imitations are still very effective and important.

Fishing imitations of these large perlid stoneflies requires a bit heavier equipment than you might use for most of your trout fishing. I find a six-weight rod just about ideal for casting the large weighted nymphs or the large more wind resistant dry flies. The best nymph fishing occurs in the week or two prior to adult emergence when nymphs are migrating to shore. But because younger nymphs are available all year long, a nymph pattern can work in any season on streams with large numbers of these stoneflies. For imitating mature nymphs a size 8, 3XL or 4XL hook is about the right size. However, I find that a size 12 or 10, 3XL nymph works best for imitating immature nymphs. I also prefer more suggestive nymph patterns, like a Brook’s stone, over the more exact imitations some people tie. The specific pattern, however, is less important than getting your fly where the fish are. Make sure you get your nymph patterns on the bottom. This means weighting the flies and often adding split shot to your leader as well. Cast upstream and across so the fly drifts naturally through good holding water in riffles and runs. When nymphs are migrating to shore make sure you fish water near the bank. That’s where the nymphs and feeding fish are often concentrated. A strike indicator will help detect strikes, but trout often take these flies with a real rush, perhaps because several fish are trying to be the first to get to it.

Egg laying adults get most active in the late afternoon and evening. This is a great time to switch to dry flies. When adults are plentiful, however, dry flies can work anytime of day, particularly on breezy days when adults get blown into the water. A wide variety of adult patterns have been tied to imitate these large stones. In fact I think just about anyone who ties flies eventually sits down and ties their own version, or several versions, of a large stonefly adult. A size eight golden brown stimulator is a very popular pattern on many western streams. Fishing these big dry flies doesn’t require a lot of finesse. As mentioned adults often make a commotion on the surface. As a result it’s okay if your dry fly slaps the water and makes some disturbance. This should be within reason of course. If you find this approach isn’t working then a more traditional dead drift presentation should be used. Because adults hangout on streamside vegetation, your best areas to fish will be near the bank where vegetation overhangs the water. This is especially true on large rivers. On small streams just about any spot that holds fish should be covered with your dry fly. Strikes can be tremendous explosions or gentle swirls, but it’s hard to miss the rise to such a large golden nuggets.

Patterns for Perlids:
Brook’s Stone (with bead head)
Hook: 3XL nymph hook, size 12-8
Thread: Gold
Weight: 6 to 10 turns of lead wire.
Tail: One Pheasant tail fiber each side of hook shank.
Rib: Copper wire.
Body: Brown to gold dubbing wrapped to middle of hook shank.
Hackle: Dark brown rooster hackle of medium quality.
Thorax: Dark-brown dubbing. Wrap four or five turns of hackle over thorax.
Note: This fly can be tied with or without a bead head. The bead adds some flash and additional weight to help sink the fly to the bottom.

Golden Stone Stimulator
Hook: 3XL dry fly hook, size 12-8
Thread: Gold
Body Hackle: Light brown rooster hackle. Palmer over body.
Body: Brown to gold dubbing wrapped to front third of hook shank.
Wing: Light tan or brown deer hair
Hackle: Dark brown rooster hackle.

Rick Hafele headed west from Illinois with the hope of striking it rich. The great western trout streams haven’t disappointed him as he has found the golden stone and numerous other western hatches a rich environment for an entomologist and fly fisher.