Beyond the Big Stones

By Jeff Morgan

The big guys get all the attention. Magazines devote page after page to the Shaquile O'Neils of the river: salmonflies and golden stoneflies . Anglers grow glassy-eyed at the thought of casting big flies for hungry trout on brawling western freestone rivers.

And while anglers focus their gaze on these conspicuous insects, trout--especially those that inhabit small and medium sized streams--are often looking somewhere else.

From May through July, two of the most important bugs on smaller streams are the little yellow stoneflies (Isoperla) and little green stoneflies (Alloperla, and other members of the Chloroperlid family).

While salmonflies and golden stoneflies are well publicized, they are abundant in only a few western rivers. On the other hand, the small stoneflies are much more widespread. Further, their emergence and availability can last 30-60 days on a particular stretch of river.

Little Green Stoneflies

There are several genera of little green stoneflies (Chloroperlid family) throughout the United States including Alloperla, Sweltsa, Paraperla, Utaperla, Triznaka and Suwallia, among others. While the diversity may look daunting, I would lay good money that even expert anglers can't differentiate between these genera in the field. I sure as hell can't.

This is good news for tiers. The genera are so similar that a handful of patterns in two shades and three sizes will cover nearly all the bases.

Chloroperlid nymphs inhabit the leaf packs that accumulate in slower riffles and eddies, and you can do well imitating them at the ends of riffles and along current seams between fast and slow water.

I mostly use are small brown patterns to imitate the nymph stage, though I like to tie up some little Chartreuse nymphs for those places that are inhabited by the bright-green colored nymphs; make you match your materials to the natural insect (when both are wet).

Even where they match the natural insect, the bright green nymphs aren't much more effective than a standard Hares Ear . The exception is during periods of high water, when many of these nymphs migrate to escape the pounding sediments. During these conditions, the bright nymphs can fish exceptionally well while the standard colors can go untouched.

Unlike other stoneflies, Chloroperlids don't make a big migration before emergence, so there is no two-week pre-emergence "nymph fest" like there is with salmonflies or golden stones.

Imitating adult Chloroperlids is a lot of fun, and can be as simple as using a yellowish-green Elk Hair Caddis pattern. Their swift water habitat alleviates the need for perfect imitations, though flies that float low are certainly more effective than others. Fishing the adult imitations near shoreline brush is very effective--that's where most adults reside during the day.

While fish will rarely feed selectively on Chloroperlid adults, I have always had much more success imitating them when using a fly with chartreuse or even slightly green imitations, rather than the standard-issue yellow advocated by most writers and anglers.

There is no doubt that the bright eggs on the end of the female adult can be a focus point for feeding trout. In a 1998 study in Wyoming, the chloroperlid, Sweltsa lamba, made up 43% of all stoneflies in the summer diet of brook trout. This is impressive enough, as there were 19 different species of stoneflies recorded. Even more noteworthy, females were consumed at a ratio of nearly 7:1! It should be noted that the eggs are not an "egg sac;" rather, they are eggs showing through the thin abdominal wall.

I always make it a point to add a red butt to the end of any adult Chloroperlid pattern, to imitate the egg-filled region. A sunken adult pattern (often just a yellow Soft Hackle ) can work too, and I add a red butt to these also. The only insects that intentionally come close to the water are females, and they all carry eggs.

Little Yellow Stoneflies

Nymphs of the little yellow stoneflies (genus Isoperla) are aggressive predators that crawl actively looking for midge and black fly larvae to prey upon. They are caught in the drift at a higher proportion than their abundance on the bottom, so it is important not to overlook them.

Isoperla is a fast-water insect that is most common on small to medium-sized streams (which usually receive less fishing pressure). Also, they emerge when there is a ton of other insect activity going on. Therefore anglers need not fret over exact imitation. If you are close, the trout will give you the benefit of the doubt.

Trout aren't particularly selective when it comes to Isoperla nymphs, for they are most common in swift water where leisurely inspection is not an option. What is important is that the nymph be presented deep, is the right size, and is approximately the right color.

The nymphs don't grow much between February and emergence, so only one or two sizes should get you through the majority of the productive season. A medium-sized bead-thoraxed nymph with rubber legs is a fine imitation.

One other thing of note with the nymphs and adults of both green and yellow stoneflies: keep them thin and long, like the natural insect.

Don't let the fact that many anglers call the adults of this insect "Yellow Sallies" confuse you. These are not as yellow (or chartreuse) as the other "Yellow Sallies" (the Chloroperlids), for the coloration is different and their adult activity often occurs at a different time. The adults of Isoperla have a darker, almost golden-yellow hue. While not as dark as golden stones, they are not as faint as the Chloroperlids. They are also larger than Chloroperlids, with most specimens best imitated on the same size 12-14 Dai Riki 270 hook as the nymphs. Moral: snag a real insect and match its size and color.

A good rule thumb when imitating adults of Isoperla, or any other adult stonefly for that matter, is that unless there is a lot of egg-laying activity or mating swarms, don't waste time fishing mid-stream. Go ahead and probe the middle of the river with a couple of casts to check the response of fish, but concentrate your efforts in areas of overhanging trees or brush. I would compare adult stonefly imitation to terrestrial fishing, where 90% of your action is within ten feet of the banks.

The CDC adult imitation is perfect as it floats low and maintains a thin profile. A yellow Elk Hair Caddis , often touted as an effective imitation, can have a profile that is 3 times as wide as the natural. The CDC is easy to tie, has a better silhouette, floats better and rides lower than the Elk Hair, so it is really a no-brainer for these small stoneflies.

Patterns

Click the links below for tying instructions:

EZ Alloperla
Sunk Alloperla
Isoperla Nymph
CDC Isoperla

Jeff Morgan has written many articles for Westfly, mostly on entomology and fly tying. He is the author of An Angler's Guide to the Oregon Cascades and Small Stream Fly Fishing.