Small Brown Stoneflies
By Rick Hafele and Dave Hughes
It was a cold day not far past the winter solstice. Other than the dark green pine boughes, and the lighter green of the river, the only colors were gray, white, and black. The gray was in the sky, and the white came from the snow that lay two-feet deep right up to the river's edge. The small insect crawling across the snow supplied the black tint.
The insect briefly took flight, then settled on quiet water about five feet from the bank. Within a few seconds, the nose of a 18-inch trout quietly broke the surface and the black bug disappeared.
It would have been easy to miss this incident. The black insect had few companions and, like most winter anglers, my senses were prepared for midges and blue-winged olive hatches. That's why it's easy to miss an important but less prolific insect: the little brown stonefly, sometimes called the winter black stonefly.
The Small Brown Stonefly Group
An insect that fly anglers call "black" belongs to a group of brown stoneflies; that's one of the quirks of aquatic entomology that we just have to accept. "Small Brown Stones" refer collectively to four distinct families of stoneflies: Nemouridae, Taeniopterygidae, Capniidae, and Leuctridae. These four families can be conveniently lumped together as Small Brown Stones because of their similar appearance and habits. They are a particularly numerous and diverse group in Western streams.
With such a diversity, hatches of small brown stones occur at many times of the year. The best hatches happen February through April, so winter is when they are most important to fly anglers. Even on a cold February day, small brown stones can be active and abundant enough to bring up a few fish, especially in the afternoon when the air is warmest.
Mature nymphs and adults of small brown stones range in size (excluding tails) from 1/4 to 1/2 inch long. Nymphs tend to be a uniform light to dark chocolate brown. Many adults follow a similar color scheme, but some may be black (called "winter blacks" by some anglers) while others are orange or reddish-brown.
Nymphs live almost exclusively in running water, although a few species occur in high mountain lakes. Moderate to small mountain streams typically have the largest populations of small brown stones, but they can also be abundant in large rivers. Most species prefer areas of moderate current with a bottom of large gravel or cobble. Nymphs feed heavily on wood debris and leaf litter. Areas where detritus collects around rocks and gravel provide excellent habitat.
Nymphs remain well hidden among bottom debris most of the time, so they are not a common food for fish until they are mature. Then they crawl out of the water and emerge on protruding rocks or logs. During these emergence migrations, many nymphs will be washed into the current and become easy prey for fish.
The wings of adults range from light smoky gray to gray with black mottling. Some species, primarily males, have short wings or no wings as adults. While these adults can't fly, they can crawl quickly over the ground.
Adults are small, unobtrusive, and easily overlooked--unless they happen to be crawling over a snowdrift. Adults mate on the ground or streamside foliage a few days after emerging. Ovipositing females do not form large swarms, however. Instead they oviposit sporadically throughout the day, attracting little attention from unobservant fishermen. Trout, however, seldom miss the opportunity.
Patterns and Tactics
While brown stones are important in two stages, nymph and adult, they are usually important in only one place: close to the river bank.
The first important stage is when the nymphs make their migrations from their midstream, river-bottom habitat to the banks. Once they're near the bank, they hang around in the water for a time, then crawl out for emergence. Lift a few streambank stones in late winter or early spring, and you'll see them there, gathered in little colonies that scuttle away from the light when you hoist the stone out of water. Trout follow these migrations, and feed on the naturals in the soft water in among inundated willows and boulders.
After the nymphs crawl out to emerge, the winged adults tarry on the terrestrial side of the same bankside environment. They are busy little fellows, moving quite agily when the slightest warmth revs their biological motors. They'll fall to the water, or make little sorties over it to lay their eggs, and trout will take them right where they took the nymphs: in the soft water along the banks. You need to be extraordinarily watchful to notice that this feeding, surface or subsurface, is happening. Then it's not difficult to match it. A size 12-14 Elk Hair Caddis in dark brown or black will usually do the trick.
An upstream or up-and-across presentation often works well for nymphs. Present the fly along pockets and edges of moderately fast riffles. Even though the fly is near the surface a strike indicator can help significantly in detecting strikes.
Polly Rosborough, in the classic Tying and Fishing the Fuzzy Nymphs, describes fishing small brown stone nymph patterns at a dead drift just under the surface, and it may be that it is not necessary to weight these nymphs. His Little Brown Stone Nymph was designed for this type of fishing.
Besides dry flies and nymphs, Soft Hackles can produce well during a hatch of small brown stones. Two of my favorite patterns are the Partridge and Orange with fur thorax and the Pheasant Tail. Apparently small brown stone adults float poorly and often sink just below the surface. Soft Hackles make excellent imitations of the drowned adults.
Fish your Soft Hackles in the same areas as the dries: along the banks and under overhanging vegetation. Cast across or slightly down-and-across, and mend line to keep the fly from dragging across the current.
It's often a wise strategy to fish a nymph as a dropper beneath a dry. Cast this tandem rig along the banks, especially where high water works back among willow and alder roots and boulders that might normally be above water. That's where trout are most likely to feed actively on either stage of this insect group.
Rick Hafele is a professional entomologist and fly fishing writer living in Gresham, Oregon. His most recent book is Nymph Fishing Rivers and Streams. Rick's good friend Dave Hughes is fly fishing's most prolific author, with over 30 books to his credit including Trout Flies. Together they are the authors of Western Mayfly Hatches.