To most fly'¨fishers, any mayfly hatch is cause for celebration. The purity of a cast that matches the rhythm of a rising trout is a treasured experience regardless of how often or how long you've been fly fishing.
While mayflies and dry-fly fishing are nearly synonymous among fly fishers, it is a rather sobering fact that these distinctive insects are usually smaller than size 14, and of dozens of different species, only three with broad distribution are large and important enough to be called "drakes." I wrote about Green Drakes and Brown Drakes in previous issues of Fly Fisherman. Green Drakes have a reputation as the premier mayfly event of the season based primarily on their size and their ability to incite foolish feeding behavior even on some of the most pressured trout water. Brown Drakes are even larger insects, but with a smaller distribution so fewer fly fishers encounter them.
A downside to both hatches is a relatively short emergence duration, which usually lasts no more than a few weeks. Also, Brown Drakes are particularly susceptible to disruption from colder temperatures and wind.
Less known, even to the point of obscurity in some instances, is a mayfly of roughly equal size to Green and Brown drakes, but with considerably wider geographic range, and a duration that often lasts all summer. There are visual differences among the three drakes, but it is the behavior of Gray Drakes that may explain a lack of notoriety that is mostly unjustified.
Look to the Banks
Most fly fishers who pay attention to hatches understand that the majority of mayflies rise to the surface as they undergo the transition from nymph to dun. This type of emergence causes the insects to be well distributed on the water and keeps them constantly available to foraging trout until the duns take flight.
Commonly known as Gray Drakes, nymphs from the genus Siphlonurus only occasionally hatch on the surface in this typical mayfly fashion. Their primary pattern of emergence is to crawl onto shoreline rocks and vegetation, and then hatch in a manner more often associated with stoneflies. As a result, Gray Drakes do not usually appear on the water in great numbers until mating is complete and the females return to lay eggs on the surface as spinners.
As a result, Gray Drake hatches often go largely unnoticed by those with eyes trained mostly on open water. What is often overlooked are sporadic but aggressive riseforms that appear within a few feet of the bank. What is happening in this situation is also commonly observed with giant salmonflies when freshly emerged adults fall to the water with wings that are not yet dry or functional for flying. Wind also plays a role in carrying the newly winged insects to the water, much like what happens with terrestrial insects.
My experience has shown, however, that the right combinations of light and weather can cause Gray Drakes to hatch prematurely during their migration to the water's edge. Almost invariably, this type of instream emergence takes place no more than a dozen or so feet from the bank, and a cool, overcast day seems to increase the likelihood.
While I have never witnessed a widespread appearance of Gray Drake duns, there have been times when a constant trickling of freshly emerged size 10 or 12 insects along the riverbank has tempted the attention of trout away from more numerous but smaller mayflies like Pale Morning Duns. In these perfect hatching conditions, a relatively sparse number of larger Gray Drake duns may be masked by a heavier volume of other mayflies emerging conventionally.
Because the seasonal emergence of Gray Drakes can encompass all of the summer months, their tendency to share the water with a changing variety of competing insects greatly exceeds Green Drakes or Brown Drakes, which are concentrated into a comparatively brief emergence period. For this reason, a selection of Gray Drake patterns stays in my vest from early June through September.
Depending on the weather or the point in the season, the timing of emergence can vary from late morning through early evening.
In the dun stage, Gray Drake is a reasonably accurate description when the insect is viewed casually at a distance. However, a slight olive tint shows up upon closer examination, and sometimes causes this fly to become confused with Green Drakes, which are often similarly sized. And while a side-by-side comparison reveals distinct differences in the coloration of body, legs, and wings, this case of mistaken identity may also explain why Gray Drakes have failed to establish a more notable individual identity.
Getting their Attention
Adding even more misunderstanding to the subject is a somewhat radical change in color when Gray Drakes enter the spinner stage. The rusty brown color of the spinner stands in stark contrast to the gray/olive coloration of the dun, and to the untrained eye, Gray Drake spinners are sometimes confused with Brown Drake spinners. But Brown Drake spinners have three tails, Gray Drakes have two. Brown Drakes are usually at least one size larger, have mottling in their wings, and don't have the reddish color of Gray Drake spinners. These are key differences that reinforce the wisdom of close-up inspection before selecting an artificial.
The behavior of Gray Drake spinners is in complete contrast to duns in respect to their appearance on the water and availability to trout. While the duns do attract interest from some larger bank-feeding trout, their sparse and sporadic appearance does not create fast dry-fly fishing.
Just the opposite is true during a late morning or evening spinner fall of Gray Drakes when the water can actually become overloaded with too many naturals. At times like this, it can appear as though every trout is looking up, and the prime difficulty for fly fishers is overcoming competition for the trout's attention when your imitation is lost among the multitude of actual insects.
Fortunately, these super events are the exception rather than the rule, but a Gray Drake spinner fall can generally be counted on to distribute large food items across the surface.
Although lower in the order of importance to many fly fishers, Gray Drake nymphs migrating to the water's edge prior to emergence represent an attractive opportunity for subsurface action. Sight nymphing in clear, shallow water near the bank is a rewarding method of filling time that might otherwise be spent simply waiting for something to rise.
Fishing a Gray Drake nymph along the banks from a boat can also capitalize on a familiarity factor that helps to simplify pattern choices in waters hosting a population of the big mayflies. This is especially helpful for river guides who cannot afford to rely on guesswork while assisting expectant and sometimes demanding clients.
Choosing a Pattern
Because of their unusual emergence process, it's rare to need emerger patterns when fishing Gray Drakes. However, it is prudent to carry a few emergers for those occasional times when significant numbers are found hatching directly from the water.
The dark brownish gray nymphs are slender in comparison to Green Drakes or Brown Drakes, and they are agile swimmers. Quick, short strips of the line and a little manipulation with the rod tip help duplicate the darting motion of the natural when fishing Gray Drake nymphs. Although I prefer a nymph tied with turkey tail fibers for this hatch, a fur-dubbed body in the correct color is quite acceptable.
Perhaps the most important point of attention when tying Gray Drake duns and spinners is the distinct separation of color between the two stages. The rusty brown and somewhat slimmer abdomen of the spinner is in distinct contrast to the more portly grayish olive dun.
As with most hatches, water type dictates the pattern style for floating Gray Drake imitations. For the most part, this applies to the amount of hackle used to support the fly. A quick, choppy current justifies several more turns of hackle.
For realism, I like the delicately marked back feathers from a Hungarian partridge for spinner wings, but CDC does a better job of flotation. A Rusty CDC Paraspinner incorporates radiating hackle fibers as a very functional suggestion of spinner wings, while providing excellent support for the fly. And on exceptionally calm water, hackle is not always required.
Many of these same factors apply to dun and emerger patterns, with key differences being color and wing position. Fully or partially spent wings are usually associated with spinners, while patterns relating to emergence are typically mounted in a more upright position.
In most instances, I rely on CDC for wings on dun and emerger patterns, but hackle is a frequent addition. A biot abdomen and dubbed thorax are used almost exclusively for my floating Gray Drake imitations.
Where are They?
In their landmark book Selective Trout, Swisher and Richards wrote that Gray Drakes are found at elevations from 3,000 to 5,000 feet. Others, such as Ernest Schwiebert and Fred Arbona describe finding Gray Drakes at considerably higher elevations. However, all of the aforementioned writers also describe Gray Drake hatches in Yellowstone Park rivers that flow at 6,000 feet or above.
Most of my experience with Gray Drakes is from the Henry's Fork where they are at elevations varying from 4,000 to 6,500 feet. The Yellowstone, Madison, and Slough Creek in Yellowstone National Park are notable Gray Drake waters that I frequent, and I have found good hatches on some portions of Hebgen Lake just outside the park, and also on the South Fork of the Madison, one of its major tributaries.
Angler friends from the trout states of California, Colorado, Oregon, and Washington have relayed stories of Gray Drake fishing on their home waters, so other Western states host significant populations as well. The primary Western species of Gray Drakes is Siphlonurus occidentalis, and in the Northeast, S. quebecensis also enjoys the common name of Gray Drake and is nearly indistinguishable in both behavior and appearance.
Slow-moving and still waters are considered primary habitat for Siphlonurus nymphs, and in general, this conforms to what I have observed in the area in and around Yellowstone. However, some of the strongest showings of Gray Drakes I have seen were in the rushing currents of the Box Canyon section of the Henry's Fork and also in the Fall River, a separate tributary with similar characteristics, which flows out of Yellowstone to join the Henry's Fork near the town of St. Anthony, Idaho. This leads me to believe that Gray Drake nymphs can find suitable habitat in the slower margins and back eddies of fast-moving rivers.
It is no mystery that big mayflies have ascended to royalty status among those with a fondness for dry flies. Like their Green and Brown counterparts, Gray Drakes have the size to attract large trout to the surface even during a relatively sparse appearance.
With easy visibility on the water, Gray Drakes allow you to use a larger hook and stronger tippets than the majority of mayfly hatches. These advantages speak for themselves when it comes to hooking and landing an exceptional prize.
Mayflies above size 14 are an anomaly on many rivers, even on the most fertile waters of the West. And like other oversize attractors of trout, they are a luxury to be savored while still retaining respect and gratitude for those lesser insects that represent the great majority of the dry-fly opportunities we typically enjoy.
René Harrop is the author of Learning from the Water (Stackpole Books, 2010) and runs his own fly-tying operation, House of Harrop (houseofharrop.com), from his home on the banks of the Henry's Fork. He wrote about Green Drakes in the Feb.-Mar. 2015 issue, and about Brown Drakes in the June-July 2011 issue of Fly Fisherman.