This is one of the most neglected mayflies in the trout-fishing world. Despite its coverage in Hafele and Hughes’s Western Mayfly Hatches, and in Knopp and Cormier’s Mayflies, the hecuba is not known to many fly fishers. The common name for the hecuba is the blue-winged red quill, but that’s a name rarely used among anglers. Most refer to it by its species name—hecuba. It is important on Yellowstone-area waters like the Snake River in Wyoming and the streams of the Lamar River drainage in Yellowstone National Park.
It emerges on most streams it inhabits from late August until mid-October, and it’s a big mayfly. Most duns are 15 to 17 millimeters long, with some specimens going 19 to 20 millimeters. I have heard it described fittingly as a “drake on steroids.” In fact, many fly fishers misidentify hecuba as a brown drake or gray drake upon seeing it for the first time. The nymphs are crawlers, but their body shape and behavior as larvae is reminiscent of clinger nymphs. They favor streams with moderate currents, yet are also abundant on some high-gradient rivers. On these waters, hecubae tend to cluster in side channels.
Emergences can be prolific, and like many mayfly species, cloudy, hecubae are out in force during wet weather. The adults are dry-bodied bugs that die from dehydration if fish and birds don’t consume them first, so it seems appropriate that cool, cloudy weather with precipitation produces mayfly hatches. I see this correlation with everything from pale morning duns to blue-winged olives. But by far, the most intense hatches I have fished during such weather events have been the hecubae.
Riffles and seams are obvious targets when a hatch is on. However, nothing is more important than fishing side channels, particularly the confluence
of side channels and mainstem channels. When a hatch occurs, hecuba emergers and duns will come pouring out of side channels and into main channels, where they are devoured by waiting trout. I have sat on confluences when a hatch is occurring and witnessed dozens of rises over a 15-minute period.
Standard larva patterns like Hare’s-Ear Nymphs and Copper Johns are commonly used as subsurface hecuba imitations. However, I have significantly more success with surface imitations when a hatch is under way.
Almost anything you use as a brown drake or gray drake imitation will also work as a hecuba pattern. The Ribbed Parawulff Hare’s Ear is just one longtime favorite. My standby pattern is Booty’s Hecuba Emerger, which features a notch piece of foam under the hackle to provide greater buoyancy on high-gradient streams. (I also use this fly as a brown drake emerger on appropriate waters.) Whatever pattern you use, go with those that are sizes 10 and 12, and be prepared to fish them when the rain falls and the clouds roll in.
Nothing tells me that autumn has arrived more than the appearance of mahogany duns on the rivers I fish regularly. Most fly fishers are familiar with those specimens that are 7 to 10 mm in length and matched with patterns that are sizes 16 to 18. These are the mahoganies found on most trout streams. But on some waters in the Rocky Mountain West, larger (and lesser known) mahogany duns are present that can completely dominate other emerging invertebrates. These bugs—of the species bicornuta and temporalis—come in at 11 mm to 12mm long and are matches with pattern
sizes 12 to 14.
I have fished a number of waters that feature the big mahoganies, including the Clark’s Fork of the Yellowstone in Wyoming, Montana’s Upper Madison
River, and the Bitterroot River in Western Montana. In my experience, emergences were always centered squarely in autumn, from the first week of September until the middle of November, everywhere I encountered them.
Like many mayflies, emergences are longer and more intense when the weather is cool, cloudy, and wet. But water temperature is the most important factor contributing to hatches. Emergences occur after water temperatures drop below 55 degrees (F.), though a hatch of big mahoganies really starts to hit its stride as temperatures close in on 50 degrees. With most streams being at low flows in autumn, you can find mahogany duns hatching in most waters types. Flats and bank margins are perhaps the most important water to target on streams with fast to moderate currents. Riffles and riffle pools, as well as seams and slow eddies, are worth investigating as well. I experience most emergences of big mahogany duns in the late morning to late afternoon hours. But again, weather plays a role. Expect big mahogany duns to appear anytime the clouds move in and rain
begins to come down on streams where the bugs are present.
The ascending nature of mahogany dun larva makes this hatch ideal for fishing with lightly weighted nymphs, either as part of a double nymph rig or a dry dropper. The classic tactic of dead drifting in moderate to fast currents produces good results. However, swinging nymphs is just as effective in slow to moderate currents and shallow holding water. For another varied effect, lift the rod tip at the end of a swing to mimic larva ascending to the surface.
Flashback Pheasant-tail Nymphs and Elk Liver Nymphs are amongst the most effective subsurface patterns I use during an emergence of big mahoganies. On the surface, I lean toward emergers like Quigley’s Film Critic and Booty’s Mahogany Emerger, and dun adult imitations like Hackle Stacker Mahoganies and Carlson’s Purple Haze or Copper Haze.
Keep in mind that fishing big mahogany emergences is very similar to fishing the smaller, more common mahoganies (debilis and memoralis) in terms of holding water and presentation. What separates them from their smaller counterparts is quite simply size. I have had enough experience with mahogany dun hatches to know that trout can and will feed selectively based on color, movement, and silhouette. Size will also come into play, and can actually be more important than other characteristics. When big mahogany duns are on the surface and dominating other bugs that might be on the water, make the switch to size 12 and 14 imitations and keep your smaller patterns in the box.
Autumn brings new experiences, every year, on just about every trout stream in North America. What sets the season apart is the arrival of new hatches, or at least, hatches anglers haven’t seen in several months. Blue-winged olives, the renewed importance of chironomids, and the appearance of October caddis, hold a dear place in the hearts of most fly fishers who target autumn with vigor. But keep in mind these “other” emergers can be even more important than those ordinary standbys of the season. Study the streams you fish, or are planning to fish, and find out if the mutant stone, hecuba, and the monster mahoganies play a role. If they are present, learn more about the behavior of these bugs and how best to fish their imitations. Your autumn outing might be better than what you planned for.
Boots Allen is a fly fishing guide and writer who lives with his wife and two kids in Victor, Idaho. His latest book is Finding Trout in All Conditions (Westwinds Press, 2015).