These are highly specialized nymphs that can dart minnow-like in the calmer waters when not perched on the shafts of aquatic vegetation or on the slowly undulating soft foliage of aquatic growth. Most of the important species range from 7 to 12mm in body length, while those of the Baetis, who prefer riffles and faster water, average between 5 and 8mm.

They are also dissimilar to the B. baetis by their three tails of equal length. Also, remember that these nymphs prefer the slower water then their cousins the B. baetis that, like the faster flows of riffles and runs.

This nymph will lose its middle tail during the transformation from nymph to dun. Look for the hatches to be in the quiet waters of eddies, pools and the side currents of runs.

The Callibaetis mayflies are multi-brooded and up to three generations may hatch during a single season where the environment is favorable. The hatching activity will vary from species to species and the timeliness of emergence will also vary according to whether the conditions are harsh or favorable in each geographical area. This means that on some waters, these insects are important from the middle of April until well into the month of September.

Their uniquely speckled or mottled wings quickly identify the duns of this genus. Of the 28 some species, only three are considered very important to the northeastern fly fisher.

Tactics

The nymph patterns should be fished with a darting, twitching motion near weed beds, roots, boulders and the underside areas of the bankings.

The 2-tailed epeorus nymphs require fast, pure water with very little or no pollution. The nymph needs vast amounts of highly oxygenated water, which is supplied by rapids, riffles and swift, gravelly runs. They cling to the bottoms of large gravel, rocks and boulders. Their flat heads, bodies and disc-like gill plates enable them to retain their tough existence in this turbulent environment. A unique activity of these nymphs is that they will migrate to the downstream sides of rocks and boulders where they will congregate a day or so before their emerging activity.

At nature's signal, which is a water temperature of 50 degrees or more for a few consecutives days, they will escape their nymphal shucks on the streambed and rise to the surface. Once started, this nymph will hatch daily even if the springs unpredictable weather and temperatures can drop back to the forties rather quickly.

Once emergence takes place and the adult spinners will return to hover over the riffles. These mating swarms will usually occur during the warmest part of the day, between noon and 2 P.M. and during the warmest days of late spring heat of 75 to 80 degrees, these spinners will return in the late afternoon or early evening.

You should remember that these imagoes mate, oviposit and fall as spent spinners in the white pocket-water or heavy runs.

Tactics

Fish will lurk in the small eddies and the smaller pools to opportunistically feed of this free lunch. These areas are just downstream from the riffled area where the insect have completed their mating activities and when they fall onto the waters surface where the currents will carry the spent spinners to waiting fish.

Now having said the above, even though these sub imagoes usually emerge in the riffles and pocket-water, pay special attention needs to be given to the downstream heads of pools where the helpless duns are swept along to the quieter waters below.

Tactics

Imitations should be fished in a way that will effectively simulate the emerging duns. Cast across and downstream and allow the imitation to drift across the feeding lanes and various lies. When the current starts to straighten the tippet, the imitation should be forced from the bottom to simulate the rising (emerging) dun.

When duns are being intercepted near or in the surface film, fly fishers need to cast upstream and allow the fly to float drag free to the feeding fish.

Don't forget to twitch or skitter the imitation to simulate the insects struggle to free itself from its watery environment.

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