Story by Harvey Thommasen with Photography by Mike Wigle

Along the shores of the river I could see the discarded skin-shell remains of a recent stonefly hatch, where juvenile steelhead and rainbow trout were 'popping' out of the water as they fed on small midges dancing on the surface.

Farther out I could see swirls, where bigger fish were feeding with abandon. But on what? After a few minutes, I realized they were taking a large insect that fluttered slowly and clumsily over the surface. Stoneflies - the adults that had emerged earlier from the shucks along the shoreline - were out, laying their eggs in a series of awkward flights in which they dropped onto the surface , fluttering their wings and riding downstream briefly before taking off. With all this disturbance, it wasn't surprising that so many stoneflies were disappearing in violent splashes, as trout rose from the bottom to feed on them.

Looking through streamside vegetation I found an adult Giant Stonefly (Pteronarcys californicus,) clinging to the underside of a leaf.

The Giant stonefly is the largest stonefly found in North America with adults measuring 25 to 50 cm (1-2 inches) in length. It has a dark brown back, and its undersurface is usually salmon red - hence the common name used by many anglers: Salmonfly.

Heavily veined, dark gray wings lie flat over its cylindrically-shaped body. There are three body segments (head, thorax and abdomen), and three pairs of well developed, segmented legs. Like most stoneflies, the eyes are widely separated, there are two well developed antennae, two tails, and two pairs of wings.

Pteronarcys californicus is one of 60 or so kinds of stoneflies found in the coastal streams of the British Columbia. Stoneflies are one of the most common aquatic insect inhabitants of the coastal streams.

Stoneflies range in size from 5 to 40 mm long (hook size #20 to #2) in length. The nymphs and adults come in various shades of yellow, orange, brown and black. Immature stoneflies are called nymphs.

Nymphs resemble the adults except for the fact they do not have two pairs of fully developed or partially developed wings, and their sexual organs are not fully mature. Close examination of the nymphs will often reveal "gills" located along the sides, or undersides of the thoracic and abdominal segments. There is no pupal stage, as the adult emerges directly from a nymphal casing.

Nymphs hatch from eggs that have been deposited by mature, female adults. Larval development takes from 6 months to 3 years, depending on species. The Giant Stonefly takes the longest time to develop - 2 to 3 years depending on water temperature and food conditions.

By day, nymphs are usually found underneath stones and other woody debris, at night they come out from there hiding places to feed. Most kinds of stonefly nymphs eat rotting leaves, some are algae grazers, and a few kinds are primarily carnivorous.

The Giant Stonefly nymphs are gentle giants of the aquatic insect world. They eat the alder, birch, cottonwood leaves and other debris that accumulates around the bases of rocks.

Each stonefly species has its own characteristic, and predictable hatching period. The first stonefly hatches begin during January and February, and they continue to emerge until late summer and late fall .

The hatching period for the Giant Stonefly is from mid to late April to mid June - typically when water temperatures get above 9.5 C (49 F).

The emergence of the Giant Stonefly is fairly typical of all stoneflies. When ready to transform into a mature adult, the nymphs migrate from their boulder strewn, fast riffle habitat to the shallows and eddies along the shore. They then crawl onto the shore, out of the water. There the nymphal outer skin is split, the adult emerges from its "nymphal shuck" and takes refuge behind rock, a log, or more often among the branches of the streamside vegetation. There, among streamside vegetation or boulders, the adult stonefly will spend most of its short life.

Although most stoneflies can fly, they are so clumsy they often remain motionless or run, rather than fly, which is why you can bend over and catch them so easily when you see them at streamside.

For the Giant Stonefly, emergence usually takes place in the late afternoon or early evening. For other species it can take place any time of the day or night. Again, each species seems to have its own preferred emergence time, and time for mating after emergence has taken place. Adult lifespan is highly variable among species, generally ranging from a few days to about four weeks. Adults have functional mouthparts and most species have the capacity to eat algae, leaves, or flower pollen. However, eating is not a priorty for adult stoneflies. Mating is far more important. As a general rule, mating takes place several days to a week after emergence.

The Giant Stonefly will spend a week or two hiding in the dark sheltered shadows among the streamside vegetation, before the male goes looking for a female to mate with. Presumably this waiting period has something to do with maturation of sexual organs.

Some kinds of stoneflies mate during the day, others mate only at night. The Giant Stonefly mates during the day, and it is not uncommon to find male/female pairs that have become "stuck" together. Mating is simple. Once the Giant Stonefly male finds a female, he climbs on her back, drapes the lower half of his abdomen around hers, and their genitalia temporarily "lock" together.

Shortly after mating, the females lay their eggs, in a dance that stirs the hearts of trout and fly fishermen alike.

Rainbow trout love stoneflies, especially the Giant Stonefly. Trout eat stoneflies all year round, and both the nymphs, and the adults are utilized as food. Since stoneflies like the Giant Stonefly take several years to develop to maturity, these insects are among the most important winter foods for trout.

Trout eat nymphs that have lost their footing and are helplessly floating down the current. They feed ravenously on nymphs that are actively migrating to shore prior to adult emergence. They feed on mating adults which clumsily fall into the water, and they feed on egg-laying females. And fortunately for the flyfisher, much of this feeding takes place during the daylight hours of the most pleasant weather days.

There are many different Pteronarcys nymph (Montana Stonefly) and adult imitations around. As long as they conform to the general size and color of the real thing they will trigger violent underwater strikes or thrilling surface rises.

Fishing on the Bella Coola River in the spring, when cutthroat are feeding heavily on migrating salmon fry, I find I can stir a surface take by tying on a Giant Stonefly imitation. Using a pattern adapted from others, which my daughter Amy has dubbed a "Floating Bugger", I will take not only cutthroat, but also Dolly Varden, a char which doesn't usually come up for a dry fly. Because of the numbers of fish I take, and their aggresive strikes, I use a bubble packing material to imitate the wings. It also makes the fly easier to see in the fast water.

The Floating Bugger pattern is simple:

Tail: deer hair

Body: Any kind of orange material

Wing: Bubbly packing material cut to shape.

Hackle: Badger Hackle

Nymph imitations can be fished in an upstream dead drift fashion - to imitate insects which have lost their footing and are being carried helplessly down stream in the current. Or they can be worked downstream and across to the shoreline - to imitate nymphs which are actively migrating to the shore.

The adult imitations can be fished in a drag free float fashion, or with short skittering movements across the water surface. They can even be deliberately splashed onto the water surface without fear of frightening the fish away.

Given all this, it seems almost as if God took into account the needs of flyfishers when he designed the stonefly.