Paraleptophlebia Anyone?

Abundant but not flashy, the late summer and fall hatches of Paraleptophlebia can be the perfect tonic for moody trout.

If any time of year produces challenging fishing conditions it is late summer and early fall. In heavily fished waters by this time of the year trout have seen enough fly patterns to write their own book. Add to this low clear water conditions where 6x tippet looks like string on mirror, and warm water conditions that put trout in a feeding stupor for a good part of the day, it’s not hard to understand why anglers have refined the art of “stretching the truth” when it comes to reporting results for the day. On days like this rather than keep fishing my old favorite hot spots where all the fish seem to have disappeared, I like to search for water less fished or for hatches less seen. This is when I like to sit on a high bank with a pair of binoculars and scan eddies, or backwaters for the less obvious hatches and some trout with food on their minds. One of the insects I keep a particular lookout for during these challenging times is Paraleptophlebia – a common mayfly in most trout streams. Wherever I find their somber colored duns, I usually find some feeding trout as well.

Paraleptophlebia (para-lepto-phle-bia) is quite a mouthful to pronounce, which might explain the wide variety of common names used by anglers to describe this genus. For example, the following names have all been used for various hatches of Paraleptophlebia: slate-winged mahogany dun, dark blue quill, little western red quill, western blue dun, blue dun, blue quill, dark brown spinner, iron blue dun, little summer quill, pale summer quill. For the sake of simplification, I will stick with slate-winged mahogany dun, as it seems to fit for most hatches, and is probably the most frequently used.

Paraleptophlebia belongs to the family Leptophlebiidae, of which Leptophlebia is the other major genus. This family falls into the “crawler” group of mayflies. Other important families of crawlers include Ephemerellidae, Leptohyphidae (formerly Tricorythodidae), and Caenidae. Compared to the dominant hatches of the family Ephemerellidae (pale morning duns, green drakes, Hendricksons, etc.), Paraleptophlebia hatches are not as well known or understood. However, there are 39 species of Paraleptophlebia scattered across the country with good populations occurring in most trout streams. As a result this is a group one should become familiar with and be ready to imitate when they are available.

Most of the 39 species of Paraleptophlebia are only important locally with just a few species widespread and abundant. In the east and Midwest the most important species are P. adoptavia, P. mollis, and P. debilis. In the west the major species are P. temporalis, P. memoralis, P. debilis, and P. bicornuta.

Recognizing Paraleptophlebia from other mayflies is relatively easy. The most distinctive feature of nymphs is their slender forked (often called “tuning fork”) gills on abdominal segments 1-7. Nymphs also have three prominent tails of equal length. Nymphs overall appear rather delicate, especially when compared to the more robust nymphs of the family Ephemerellidae. Two western species, P. bicornuta and P. packi, have unique mandibles that form large sickle shaped tusks projecting out in front of the head. Mature nymphs have well formed black wingpads and reach lengths of six to about ten millimeters excluding their tails (1/4 – 3/8 inches). Most nymphs will be light tan to brown in color.

Adults (both duns and spinners) have three tails, a feature common to all crawlers and one that clearly separates them from the two-tailed adults of the swimmer and clinger groups of mayflies. To separate Paraleptophlebia from other look-a-like crawlers of the family Ephemerellidae look closely at their hind wings. The hind wings of Paraleptophlebia will have an evenly rounded leading edge with no hump known as a costal angulation. All species of Ephemerellidae have this raised hump on the leading edge of the hind wing. Both male and female duns of Paraleptophlebia have a rich brown (mahogany) body color and solid gray wings. Color, however, often differs between male and female spinners. Females retain a uniform reddish brown color. The males of many species, however, have a dark brown thorax and nearly clear white abdomen that gives them an almost ghost-like appearance when dancing in mating swarms over the water. (Note: males of P. adoptavia remain a uniform reddish brown color like the females.) Like the nymphs, duns and spinners range in length from six to just over ten millimeters excluding tails.

Paraleptophlebia are stream dwellers. However, during their growth as nymphs their habitat preferences change slightly. Young nymphs spend most of their time in moderate to fast riffle areas. Then as they mature they move to areas of slower current. Mature nymphs are most abundant in glides, slow moving backwater areas, and slow water along the edges of the stream. In spring creeks, where Paraleptophlebia are often abundant, mature nymphs concentrate in areas with slow currents and thick growths of aquatic plants. Because mature nymphs prefer slow currents, the best hatches will be found in backwater areas and slow moving flats.

Like most crawlers Paraleptophlebia nymphs are not fast swimmers when compared to true swimmers like Baetis. Nymphs prefer to stay hidden among aquatic plants or other debris on the stream bottom, but when they find themselves in open water they move with a snakelike side-to-side wiggle. Their progress is relatively slow, and it is easy to see why they find slow currents preferable. Despite their poor swimming ability, nymphs become quite restless just prior to hatching and often make several practice swims towards the surface for up to an hour before they actually emerge. Finally the nymphs leave the bottom for good and swim slowly to surface where the duns emerge in the film. All this activity prior to emergence makes nymphs quite vulnerable to feeding fish.

During emergence the duns also become easy targets for fish. They often float long distances (40 feet and longer) before flying. On the smooth flat surfaces 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 depending on weather and time of year. Warm weather will push the hatch to the morning hours, while overcast or cool weather will move the hatch to the mid or late afternoon. The time of year emergence occurs varies with the species. Species like P. adoptavia and P. temporalis emerge in the spring. Other species like P. debilis and P. bicornuta emerge in the late summer and fall continuing to hatch well into October.

A few hours after emergence, spinners begin swarming and mating. Lehmkuhl and Anderson described this mating activity in detail in a scientific journal article as follows:
Within 3-4 minutes after the sun ceased shining on the water’s surface, groups of 30-40 males appeared and swarmed 2-4 feet above the water, about 2-10 feet from shore. The dance was performed by the male repeatedly fluttering rapidly upward 4-5 feet above the water, then the wings and cerci were spread, the forelegs were stretched far forward, and they floated down until they were about 2 feet above the surface. Occasionally they fell into the water and usually could not free themselves.
Females appeared about 30 minutes after the males began to swarm. When a female entered a swarm she was immediately grasped by a male. The pair lost altitude and copulation was completed in the time it took them to fall 3 feet. The pair then separated and the female immediately began skipping across the surface of the water depositing eggs. She dropped to the surface of the water, dipped the tip of her abdomen, flew about 2 feet into the air, and dropped again….. The time from the first contact between male and female until the last of the eggs were laid was only a few seconds.”

Fly Fishing Fishing Tactics

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

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

Once duns start drifting in good numbers fishing dries becomes very effective. My favorite pattern is a size 16 compara-dun with a reddish brown body and gray wing. A Harrop dun or parachute pattern also work well, but the selective nature of the feeding that often occurs during these hatches means you will want a fly pattern that closely matches the size and silhouette of the natural. The slow smooth currents where Paraleptophlebia hatch also requires 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 also 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 and early evening.

When you face tough fishing conditions this fall, take a look in some areas you generally don’t fish. Carefully watch backwaters and flats with gentle currents for the small dark bodies of slate-winged mahogany duns drifting quietly on the surface. Further observation may reveal the subtle rises of confidently feeding trout, and some exciting opportunities for fish.