When I arrived home the other evening from my time on the stream I realized I had my next topic.  The opportunity to fish a particular hatch encompasses quite a lot when you break it down and put it all back together.  It's a good part of the "stuff" I'm made of.

As I walked to the stream I envisioned this to be a good time to be on the water.  Heavy cloud cover continued to mask the late afternoon sun and air temps were in the mid-60's even though it was mid-June.  The hatch I consider the most popular of the year had pretty much been relegated to a memory with perhaps the last few Sulphur spinners making their appearance at dusk.  This day, however, I wasn't here to fish Sulphurs.  There's a bigger critter on the block right now and, while this particular mayfly never really hatches in great numbers on any given day, it usually has the trout looking up in anticipation of a wayward dun drifting on the surface.  I told Ed that I'd be serving a Slate Drake as the main course and I'd made up my mind that I'd only serve it one way:  dry.  O.K., I have to admit I had my stash of nymphs in my vest just in case but I was bound and determined to fight any temptation to use them.

Slate Drake or more recently Iso as it is called are two common names for Isonychia bicolor.  Hatch activity usually begins around the third week in May here in central and north central Pennsylvania.  Another much more famous drake makes its appearance not long after.  The Green Drake, Ephemera guttulata, is truly a mayfly that lives up to it's name.  Ephemera means short-lived and, sure enough, the Green Drake may only provide a week of good hatch activity.  The Slate Drake, however, can be active right through the month of June. 

Interestingly enough, the Slate Drake stands apart from other mayflies in that there are two distinct groups of the same species which hatch at different times:  while one group hatches early the other group makes its appearance around late August and can go right into October.  

I can hear it now.  Some folks are saying, "Wait a minute.  BWOs (Baetis) do the same thing.  They hatch in the spring and again in the fall.  And we don't call them groups, we call them broods!  So, what's going on here?"  Well, I'll tell you what's going on.  With Baetis each brood goes through a complete life cycle:  egg, nymph, dun, spinner.  Here, a complete life cycle takes but a few months.  Not so with Isonychia.  Each group's life cycle spans a full year.  For some crazy reason one group chooses to show up early and the other holds off a bit.  If there's another more scientific explanation I've never heard it.

Slate Drake nymphs are really interesting.  Well, they are to me, anyway.  They're not really what I would describe as slender;  however, they're not what I would call robust, either.  Their gills are a prominent feature as they extend out from the sides of their abdomen for most of its length.  Another distinctive feature is the prominent median stripe running from the back end of the abdomen right up to the head.  As with every rule there are always exceptions.  The exception here is that the nymphs of the late season group doesn't exhibit the median stripe.  And no, I don't have any explanation for it.   

Slate Drake nymphs  are categorized as swimmers and they're quite good at it.  They're quite jumpy, too.  When I go looking for nymphs to photograph or to show to other folks rather than use a catch net I'll just pick up rocks.  More often than not when I encounter a Slate Drake nymph it's there and suddenly it isn't.  While they don't actually jump they can move their body so forcefully and quickly that it appears as though they jump off of the rock.

Another characteristic which separates Slate Drake nymphs from the vast majority of other mayflies is their compulsion to migrate to the shoreline and crawl out onto stream to emerge.  This isn't what I call a blanket behavior.  If every single Slate Drake nymph would emerge in this manner I'd be prone to believe that we'd be hard pressed to find an exposed rock surface anywhere along the streambank.  As I walk the stream I find the heaviest concentration of nymphal shucks along the pocket water and riffle sections.  A clue to where most Slate Drake nymphs reside?  I'd answer in the affirmative. 

Slate Drake nymphs can vary in color from stream to stream.  I've captured specimens that have appeared almost black to a significantly lighter reddish-brown.  You can see for yourself as you view the images I've included in this article.  

There have been a number of times when I was standing in the stream with Slate Drake nymphs rising to the surface and emerging around me.  As with any emerging mayfly's vulnerability during this process trout recognize this activity as presenting them with some easy pickins'.  Of course this means that we just might find it beneficial to carry a few patterns representing an emerging Slate Drake.  Wouldn't want to miss out on an opportunity now, would we?  

As I stated earlier Slate Drakes just don't seem to hatch in great numbers;  rather, they seem to hatch over a longer period throughout the day.  Some duns may begin to appear as early as 2 p.m. and they can hatch sporadically until near dusk.  Even so, my experience has been that trout are on the lookout for the occasional dun.  I believe the fact that they're really big in comparison to most of the other critters they may encounter makes them all the more appealing to the trout.  As with any hatch cloudy overcast days are the best.  Trout seem to be less cautious and more willing to come out and feed throughout the day.    

So now we have a Slate Drake nymph having made its way to the shoreline and having crawled out of the water onto a rock.  The dun emerges from the nymphal shuck a couple of inches away from the water.  Its wings dry as it remains in position and then it happens.  A slight breeze blows the dun off its perch and onto the stream surface.  Trout food!


The body of a Slate Drake dun can vary in color from predominantly gray with a tinge of brown to a lighter gray-brown to anything in between.  One characteristic remains constant:  their middle and hind legs are light and their front legs are dark.  Kinda' neat, I think.

As with any mayfly the duns don't remain duns for very long.  Back in the streamside flora there's another transition that turns the duns into spinners.  This is it, folks.  It's the stage that makes the fly:  literally!  Here it's all about procreation and that's the task of the spinner.  Somehow, though, I don't think the trout really care what the spinners are up long as they come down and fall on the water.  And that's exactly what they do, eventually.


Evening brings with it like kinds of dark reddish-brown spinners gathering high above the stream at first and descending gradually as males locate females and join together.  As they separate the females deposit their eggs and there's only one thing more for the spinners to do:  die.  As they flutter their wings and wiggle their abdomens a few more times as they drift spent on the surface the trout take their time and feed at their leisure.  For sure the spinners aren't going anywhere except downstream.  Casual riseforms as trout sip spinners from the surface film are the last call to fly fishers to experience the evening's opportunities.


Some say I get a little crazy with my approach to tying hatch-matching mayflies.  I wear that badge with pride!  I choose to suggest the gills on nymphs that wear them as a prominent feature.  That holds true of my imitation to suggest the Slate Drake nymph.  It's one of my patterns that's been requested by various authors to be included in their books and/or magazine pieces over the years.  Fortunately, not only is it interesting to look at it has proven acceptable to trout over time, as well.  

Of all my flies' I've played with various body colors more with my Slate Drake nymph than any other.  And I've got to admit that I can't say one color has out produced another.  I believe all that matters is that the color of my imitation is "in the ballpark."  

Where I don't want to compromise is with the suggestion of gills.  I tell folks that I like to suggest movement where trout expect to see it.  My hope is that the more I can include that in an imitation the greater the effectiveness quotient may be.  Please note that I said "I hope."  I believe that's all we can do.


Hook:  #10 - #12 2XL nymph hook

Thread:  Uni-thread 8/0 Camel

Tails:  3 ostrich herl tips

Rib:  medium brown sewing thread

Median stripe:  white sewing thread

Abdomen:  mix of seal brown, brown, tan and chocolate brown rabbit

Wing case:  black poly 

Legs:  brown mottled hen back fibers

 Note:  dub the abdomen very tightly and wrap tightly.  Pull median stripe up and wrap rib very tightly.  to form gills run a T-pin or dubbing needle along sides pulling only a little dubbing out.  DO NOT PLUCK!  Trim to shape.  For the later group go darker on the body color and eliminate the median stripe.

For my dun imitations I primarily use a parachute.  You'll notice I like to keep my hackle sparse and right down at the base of the wing against the body.  I want the wing to be seen through the hackle.  Besides, I believe the hackle only contributes a little to fly flotation.


Hook:  #10 standard dry fly hook or #10 - #12 2XL dry fly hook

Thread:  Danville gray 6/0

Tails:  medium dun microfibetts

Body:  mix of gray and brown rabbit

Wing:  dark dun ParaPost (this stuff floats like a cork!)

Hackle:  ginger

Note:  for my cut-wing I get a little carried away and cut them by hand.  I also wrap a turn or so of dark dun hackle at the front to suggest the dark front legs of the natural. 


I have come to prefer grizzly hackle tied spent for my spinner wings.  I can tie them so the fibers spread out and give me a better wing shape when fished.  I can't stand antron or poly matting together and looking all goofy when I'm trying to fool a sophisticated trout!  Yeah, I know, like they really know the difference...


Hook:  same as dun

Thread:  Uni-thread dark brown 8/0

Tails:  light dun microfibetts

Body:  mix of seal brown and chocolate brown rabbit

Wings:  grizzly hackle tied spent using figure 8 technique.

One point that needs to be made about the later-appearing group:  they run a size smaller than the early group so drop down a size in imitations to match them.


I had an interesting conversation many years ago when I was in the process of writing an article on tying and fishing Slate Drake nymphs.  I attended an event that featured two prominent authors who, surprisingly, brought along a fly-tyer to tie their patterns.  I know, kinda' seemed strange to me at the time, too.  Somehow the fly-tyer and I got on the subject of fishing these nymphs.  When I told him I fished them dead-drift he emphasized the fact that these nymphs are agile swimmers and that anyone who didn't impart some form of swimming action to their imitations didn't know what they were doing.  And, yes, that included me.

To dead-drift a Slate Drake nymph through pockets and riffles is my preferred tactic.  I've always felt that when I impart movement - attempting to mimic the swimming action of my nymph - it would appear unnatural.  Even swimming nymphs stop swimming at times and just drift with the flow. 

The key is to manage the drift carefully.  Target your presentation - whether you use a tight-line system or an indicator system - to get the best possible drift through the current you've targeted.  I recommend fishing as short of a line as possible to manage the drift best.  Some time in the future I'll write an in-depth piece on how I present and drift nymphs.  Everybody has their own way of doing things.

When I choose to fish a Slate Drake dun I fish every type of water the stream has to offer.  While I expect the most response from trout in the faster water sections I'm not surprised when a trout takes a dun in slow water.  In faster water I'll fish a 4X tippet.  Slow water calls for a step down to 5X.  I don't like to go below 5X because of the potential for the large fly to spin a tippet so by using a longer (4' or more) tippet I usually get an adequate drift.  A lot of the time I blind cast when fishing a Slate Drake dun.  Sure, when I spot a trout actively picking duns from the surface I've acquired a target and I go for it.  Other times I'm casting to areas I'd expect a trout to hold.

Rise form is my indicator it's time to tie on a spinner imitation.  Here is where keen observation is very important.  Sometimes I'm slow to pick up on a change like this;  however, past experience has taught me that when the rise form changes I need to follow suit.  Fishing spinners is target shooting.  I pick a feeding fish and work on it.  I do my best to avoid getting distracted by other feeders in close proximity...unless I can tell another target represents a significantly larger fish than the one I've been working.

So, there you have it.  Slate Drake, Iso, Isonychia (my preference).  It doesn't matter what you call them.  What matters is that it's a great mayfly that can provide some really great fly fishing opportunities.  Get out there and fish 'em!

POSTSCRIPT:  Wednesday, June 16, 10:15 p.m.  Just returned from fishing a local freestone stream known for harboring good population of Slate Drakes.  Spinners of a few different mayflies in the air.  Chose to fish a Slate Drake spinner imitation.  Wow!  Steady surface activity with native brookies, wild browns and hatchery rainbows from 7:15 p.m. until dark!!


2 Comentarios

  1. This is a wonderful article. There is more practical information here than in most pieces on Slate Drakes. And I look. forward to this: "Some time in the future I'll write an in-depth piece on how I present and drift nymphs."

  2. It's been quite a long time, but I can still remember taking a really nice native brookie that day you and I fished for the first time on Big Fishing Creek. That fish took an Isonychia nymph. Good times!