tying

Aquatic Sowbugs

By Jeff Morgan

Aquatic sowbugs thrive in many tailwaters, and trout grow fat on them. So why are most Western fly anglers unaware of their existence?

f you've reached an intermediate level of fly fishing skills, you know about scuds. Many patterns have evolved over the past century to imitate them. No angler should be without them, either for streams or lakes. But most Western anglers are unacquainted with sowbugs (genus Isopoda), and they dwell unheralded and generally unnoticed in many productive tailwaters.

For example, in Oregon's Crooked River--a stream renowned for its scud population--sowbugs outnumber scuds in some sections. Yet most anglers, guides, writers, and shops have remained oblivious to their presence until recently.

The Same, Only Different

Most sowbugs range from 10-18 mm (3/8 to 3/4 inches) in length at maturity. At first glance, they resemble scuds, but on closer examination the differences become obvious. Sowbugs are extremely dorso-ventrally (top to bottom) flattened and their seven pairs of legs extend to either side of the body. These legs are used to crawl along the substrate or weed growth, but they are nearly worthless for swimming. Sowbugs most often have a dark, slate-gray back and whitish legs and belly. However, the color combinations can mix up black, dusky, or brown backs with yellowish or creamy bellies. Usually, one species makes up the whole of the population in a body of water, so colors and sizes are relatively constant for a fishery.

Sowbugs can flourish in slow, unpolluted tailwaters, springs, creeks, and small ponds. I used to say, "Only look for sowbugs when you find scuds," but I've changed my mind. Sowbugs are rarely found in large streams or large lakes, even when scuds are abundanct. On the other hand, sowbugs can be found in waters with no scuds, especially on rocky spring creeks with limited weed growth.

In general, however, look for sowbugs in good scud habitat: slow water with plenty of weeds is a salad bar condominium for these little critters. Besides weeds, sowbugs will inhabit streams with an abundance of leaf litter in shallow pools and eddies. In these waters they thrive incognito while anglers take stream samples in the fast riffle water only a few yards away.

One sure thing about sowbugs: they live in patchy communities. You don't find them everywhere, but they can have huge populations where they occur. In small rivers, sowbugs can become concentrated by the thousands where swift waters slow down. Below these areas trout should have bellies bulging with sowbugs!

One reason anglers tend to overlook sowbugs is that they often live just under (by a few inches) the substrate. Here they are not generally available to trout, but when anglers walk through the area, they disturb the substrate and kick up sowbugs galore. At these times, and as a stream clears after a high-water event, drifting sowbugs can be an extremely important food source for trout.

Where sowbugs are present, they provide a rich source of easily obtained food for trout. Large sowbug populations are synonymous with large trout. Knowing sowbug habits and habitat doesn't pay dividends on all waters, but knowing about them on the rare occasion you encounter them can yield plentiful, large trout.

Imitating

There are a few cressbug/sowbug imitations out there from eastern anglers and British fly tiers. Many patterns are simply dubbing wrapped around the hook and picked out on the sides. This can be all you need, though I prefer a slightly more sophisticated imitation.

One thing I have noticed is that sowbugs tend to tumble when drifting in the current. Considering the anatomy of this flat, light insect, this should not be a surprise. This drifting causes the sowbug to alternately flash its dark back and light belly. I have fished a number of imitations for sowbugs, and generally the most effective ones were flat with a dark back and light belly. They had a similar fluttering effect underwater.

To fashion a flat body, I take a standard size 12, 14, or 16 nymph hook (the only three sizes I use for sowbugs), then wrap five or six turns of .20 lead wire around the hook. I then flatten the lead wire with pliers, and super glue the flattened lead. The super glue helps keep the flattened wire together and prevents crumbling after a fish or two chews up the fly. I have tried lead tape for this, and the tape is too pliable and doesn't work all that well.

Once you have a number of flattened bodies, how you tie the fly is really up to your imagination. I like a basic white-dubbed fly with a dark gray scud back, ribbed with 4X clear mono. Once the fly is tied, I pick out the dubbing on the sides to imitate legs. That's it! A darker body can be constructed with various colors of gray dubbing and a clear Body Stretch shellback. It is an easy, realistic, and effective imitation.

Occasionally, I like a bouyant imitation to fish just above weed beds in ponds or slow rivers. With this variation, I omit the lead underbody and dub a body of white or cream-colored deer hair. I usually keep the same dark shellback and clear ribbing. With the deer hair, you can dub a moderately thick body, then flatten it with the shellback on top and some strategic snipping on the bottom.

Tactics

Concentrate your sowbug efforts in the slower runs of weedy streams. I usually fish an imitation under an indicator, more to regulate depth than to notify me of takes.

Perhaps the most deadly way to fish sowbugs is sight-fishing for trout holding in the weed-choked margins of spring creeks, though the opportunities to do so are rare. These fish can be incredibly spooky, but they are in perfect sowbug habitat, and if you put an imitation in front of them while remaining undetected, they usually take with little hesitation.

Patterns

Shavers Sowbug
Deer Hair Sowbug
Foam Sowbug

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. Jeff is currently a graduate student at Stanford University, where he is finishing his PhD in History.

Uploaded 06/26/2004.

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Shavers Sowbug, top view

Deer Hair Sowbug, top view

Foam Sowbug, top view