Anatomical Nymphs
The Skip Nymph is an all-around imitation of a mayfly nymph, and when tied in a broad range of sizes and three different colors, it effectively imitates about any mayfly trout care to eat. After 15 years of catching fish on this fly, I depend on it when I need a generic pattern to fool fish looking for mayfly nymphs. But no fly works every time—my trusted Skip Nymph included—and a more specific imitation sometimes provides an edge. That’s why I developed an anatomical series of nymphs—the Anatomical Green Drake, PMD/Baetis, and Callibaetis.
I fish mayfly hatches often enough that I like to have nymphs so convincing that I feel they can’t miss, though the term “can’t miss” is always relative in fly fishing. If I’m fairly certain the fish are taking, for instance, Pale Morning Dun nymphs, and especially if the fish are wise to anglers and their tricks, I’ll reach for an Anatomical PMD/Baetis. I often refer to the Anatomical series as my “confidence nymphs.”
When I fish an Anatomical, I never blame failure on the fly, but I always feel the fly’s realism contributes when I succeed. Anatomicals have gills. They have appropriately splayed legs. They have the correct number of tails rather than a brush of fibers. But Anatomicals don’t have the crawl-away perfection of an hours-to-construct, realistic pattern by Bill Blackstone or tying pioneer Bill Blades. I think Anatomicals are as detailed as they need be to convince careful trout—more detail would be for fishermen, not fish. Consequently, tying them is not unmanageable for average tiers.
Here are the three Anatomical nymphs and the major Western mayfly species they imitate.
Anatomical PMD/Baetis
Blue-winged Olives (BWOs) and Pale Morning Duns (PMDs) are year-round staples of Western river mayfly fishing. Small, dark brown, slender, and lightly gilled, the nymphs of these two mayflies look so similar that an imitation of one imitates the other.
BWOs hatch year-round but are most important from fall through early spring when few other mayfly, stonefly, or caddis species are hatching to compete with them. BWOs prefer cloudy, even foul, weather (though they will hatch in sunshine) and typically appear between 11 A.M. and 4 P.M. To imitate BWOs I fish Anatomical PMD/Baetis nymphs in two ways Right along the bottom in the hour before the hatch, when the trout know to look for the active nymphs; and near the surface, dangling from the bend of a dry fly’s hook on 8 or 10 inches of tippet, to rising trout that seem to want neither an emerger nor a dry fly.
PMDs are generally the longest- and strongest-hatching summer mayflies on Western rivers. Like BWOs, they prefer cloud cover but also hatch briefly in the sunshine. They hatch from around 11 A.M. to 1 P.M., but later in the season they hatch in the earlier and later hours, lying quiet during the hot part of the day. They return to midday hatching in the fall. When there is no hatch in good PMD water, I often fish my Anatomical PMD/Baetis as a dropper above a heavy stonefly nymph in riffles and other lively currents. But an Anatomical PMD/Baetis fished a few inches below a dry fly can be just the thing when duns are hatching and trout are up feeding on them.
Anatomical Callibaetis
Of all the mayfly species that live in North American lakes, Callibaetis are the most common and widespread. They abhor sunshine and rarely hatch without cloudy or even rainy skies. They normally hatch from around 10:30 A.M. to early afternoon, but I’ve also seen them coming off into the evening hours, with trout feeding on them the whole time. Callibaetis produce up to three broods in a season; the first in early spring is large (#12), the second in early summer is smaller (#14); and the fall hatch smaller yet (#16). I try to keep plenty of #14 nymph, emerger, and dry-fly imitations on hand—the trout always seem to take this size, regardless of which brood of Callibaetis is hatching.
When trout are rising during a Callibaetis hatch, a dry fly or emerger makes perfect sense—yet the nymph can sometimes outproduce both. When the trout prefer nymphs, I fish my Anatomical Callibaetis from just under the surface—so it’s nearly exposing its wingcase—a foot or two below the surface with a slow and varied hand-twist retrieve. Before the hatch, an Anatomical Callibaetis fished near weedbeds can stir up some action. In clear, weedy lakes—the best Callibaetis lakes—when nothing is hatching, I often cast or troll an Anatomical Callibaetis on a fast-sinking, full-sinking line.
Anatomical Green Drake
Fly fishers dream of catching heavy trout on big Green Drake dry flies. And dry flies do work, but sometimes—as with most mayfly hatches—nymphs are best. A Western Green Drake nymph is something of a brute—fluffy gills line its stout abdomen and its powerful-looking legs emanate from its full thorax that appears somewhat hunched beneath its wingcase.
Western Green Drakes emerge from late spring through summer from fast water on overcast afternoons, typically from 11 A.M to 4 P.M.
I’ve not forgotten that the Skip Nymph series has caught lots of tough trout across the U.S., in Canada, and overseas. And I still think it is the best choice when I’m not certain what the trout are taking—after all, impressionistic nymphs may suggest several possibilities, increasing the odds of covering the correct insect. But if I’m convinced the trout are onto the nymph of a specific mayfly species, please hand me an Anatomical.
Skip Morris is the author of more than ten books on fly fishing and tying. His latest is Morris on Tying Flies (Frank Amato Publications, 2006).
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