Mahogany Duns

By Rick Hafele and Dave Hughes

Paraleptophlebia is a diverse genus belonging to the family Leptophlebiidae. Twenty species are present in the West, six of which are quite common and widespread: P. temporalis, P. bicornuta, P. gregalis, P. debilis, P. heteronea, and P. memorialis. Identifying the different species is not necessary for fly fishing purposes, however. Common names include mahogany dun , blue quill, blue dun, and just plain "paralep."

Habitat and Life Cycle

Paraleptophlebia nymphs are stream dwellers. They are easily identified by their "tuning fork" gills. Young nymphs spend most of their time in moderate to fast riffles. As they mature, they move to areas of slower current. Mature nymphs are most abundant in glides and still backwater areas. In spring creeks, where Paraleptophlebia are often abundant, mature nymphs concentrate in areas with slow currents and thick growths of aquatic plants.

Nymphs become quite restless prior to hatching, and may make several practice runs towards the surface. This activity normally begins in the mid to late morning, beginning as much as an hour before the actual hatch. Finally the nymphs leave the bottom for good and swim slowly to the surface, where the duns emerge. Throughout their pre-hatch "restlessness" and slow rise in slow water, the nymphs are quite vulnerable to trout, and many of them end up in a trout's gullet well before reaching the dun stage.

During emergence the duns also become easy targets for fish. They often float long distances (30 feet or more) before flying off. On the smooth flat surface typical of the areas Paraleptophlebia emerge from, this behavior often creates selective feeding. Look for the heaviest hatches to occur between mid-morning and late afternoon.

A few hours after emergence, spinners begin swarming and mating. Male spinners often differ drastically in color from females. Females tend to be a uniform reddish-brown, while the males often have a dark thorax with a striking white, almost transparent, abdomen. Females lay eggs by dipping their abdomen in the water immediately after mating in mid-air.

In the West, two species--P. gregalis and P. temporalis--emerge in spring, but it is P. debilis and P. bicornutta (the largest of the species) that produce the best late summer and fall hatches.

Patterns and Tactics

The low water conditions common in the late summer and fall produce excellent conditions for fishing Paraleptophlebia patterns. Nymphs should be tried first, beginning well before the duns start floating on the surface. A sparsely-dressed size-16 Hares Ear often works well. The naturals are in slow water areas, so concentrate your fishing in backwater eddies, the edges of riffles, and flats.

A straight upstream or up-and-across presentation normally works best. Strikes will usually be subtle, making a strike indicator helpful. Nymph patterns will continue to be effective during the early part of the hatch when nymphs are rising and floating near the surface.

Once the duns start drifting in good numbers, fishing dry flies becomes very effective. My favorite pattern is a size-16 Comparadun with a reddish brown body and dark gray wing. A thorax-style dry can also be effective. The slow, smooth currents where Paraleptophlebia hatch require delicate presentations with no drag. A downstream slack line cast will often produce the best results for this type of fishing.

When spinner falls are heavy they can be important to imitate. A lightly-tied Compara-Spinner with a dark brown body is generally all that is needed. Since the spinners don't become active until the sun leaves the water, look for the best spinner falls in the late afternoon or early evening.

--Rick Hafele

A couple of experiences with mahongany duns (mayflies of the genus Paraleptophlebia) point out how careful you must be when making generalizations about matching hatches in the West.

The first came one September on the Yellowstone River, in the Park. Trout appeared to be sipping blue-winged olive duns (Baetis) but we were unable to catch fish on imitations of those.

When we finally collected specimens and observed them closely--which we should have done first rather than last--we discovered the trout were taking Paraleptophlebia, which were a size larger and nearer to brown than the green-bodied flies we were using. We switched quickly, and as quickly began catching trout.

The second experience was on Yellowstone Lake, where you wouldn't expect these stream-dwelling insects to appear. One evening my wife Masako and I got into a heavy spinner fall along the edges of the lake, deep into the southeast arm, far from any stream.

I collected a specimen, noted the three tails that marked it as derived from a mayfly nymph of the crawler kind, and pickled it in alcohol to show Rick later. I had no idea what it might be, coming from a lake as it did. Masako and I matched it with simple Compara-Spinner dressings and caught trout well enough.

Long later, Rick identified the naturals as Paraleptophlebia, living where they did because constant wave action along the shore turned it into a virtual stream situation.

--Dave Hughes

Rick Hafele is a professional entomologist and fly fishing writer living in Gresham, Oregon. His most recent book is Nymph Fishing Rivers and Streams. Rick's good friend Dave Hughes is fly fishing's most prolific author, with over 30 books to his credit including Trout Flies. Together they are the authors of Western Mayfly Hatches.