Bi-Colored Iso Klink

This Klink-style pattern is designed with a specific hatch—and specific fishing challenges—in mind. In Central Pennsylvania, Isonychia mayflies, or “ISOs,” tend to be large in their adult form, often falling in the #12-8 size range. For anglers who struggle to see smaller dry flies at a distance (and let’s be honest, most of us do), that extra visibility is a real gift.

But size isn’t everything. This pattern also uses a bi-colored post for improved tracking. When Hans Van Klinken first developed the original Klinkhåmer Special back in 1984 to imitate emerging caddisflies, it revolutionized the way anglers thought about visibility and presentation. His design featured a parachute-style hackle around a high post that made the fly easy to see for the angler, while the abdomen dipped low into the water column to attract fish. That idea has since been adapted worldwide for countless species—including here, where it’s reimagined for the Isonychia.

The bright, bi-colored post on this version helps immensely in variable light. You can customize the colors depending on your preference and conditions—common combos include chartreuse and white, pink and purple, or orange and chartreuse. The high-contrast pairing helps your eyes pick up the fly on tricky water, especially when lighting shifts throughout the day.

The body of the fly is built from claret-colored goose or turkey biot, which closely matches the ISO’s natural coloration. Wrapped biot gives a segmented look with natural ribbing and translucence—traits that really sell the silhouette in clear water. The result is a high-riding, easy-to-track fly that consistently draws takes from brook trout, brown trout, rainbows, fallfish, and even smallmouth bass. It’s the kind of fly that earns a permanent spot in your ISO box.

Materials

Hook: #10 Firehole Outdoors 315
Thread: UTC 70D Rust
Body: Turkey Biot Quill in Claret
Thorax: Semperfli Kapok dubbing in Rust blended with SLF Squirrel dubbing in Rusty Brown
Hackle: Golden badger saddle hackle or rooster neck
Bi-Colored Post: McFlylon in cerise and purple.

Step 1

Start your thread an eye length behind your hook eye, flatten your thread by spinning it counterclockwise and take touching wraps down the shank and deep into the hook bend. Clip a single Turkey Quill Biot as close to the rachis as possible to ensure the longest length you can get. Break or snip off the very tip of the biot, since they tend to be brittle, and may break off when you begin wrapping the biot. Make sure the concave side of the biot is facing you when tying in, as the segmentation will only happen when you have the fibers facing you.

Step 2

Again flattening your thread to keep a smooth body, take thread wraps back up the hook shank until you land directly above the hook point. If you use an inline rotary vise, you can half hitch this spot, and put your thread over a bobbin cradle to prepare for wrapping the biot.

Step 3

Make gentle wraps at first to start and begin wrapping the biot up the hook shank. At first, they will be close together, and you will notice the segmentation begin. Keep each wrap up against the last, making sure not to cover the fibers that make the ribbing effect. If you do, simply reverse, adjust, and continue. Once you reach the spot above the hook point, cross your thread over the biot and secure it. Clip the remaining tag and smooth out the area with flat thread to prepare for the next step.

Step 4

Cut a 1” piece of McFlylon float yarn in cerise and another in Purple. If the fibers are stuck together, you can use a small underfur comb to break them apart. Align the two bundles between your fingers and cut one end to get a clean top to the yarn post. Measure the bundle to the length of the hook eye to the back bend of the hook. This will be your estimated post height. You can always shorten it later once it’s secured onto the hook. Using a pinch wrap, secure the bundle onto the hook shank making sure it doesn’t rotate.

Step 5

Cut the remaining tag to the left at a shallow angle to create a ramp for the thread to cover.

Step 6

After securing the yarn and covering the tag with flat thread, lift the yarn bundle up and build a thread dam in front of it. Continue to flatten the thread and once the post is almost vertical, you can start taking flat thread wraps around the post in a clockwise direction. Wrap your thread gently up the post until it starts to hold itself up. You can begin tightening these wraps by gently holding the yarn post with your other hand every few wraps. Stop when you are about 1/4” up the post, although I like to give myself a touch more just to give plenty of room for the hackle.

Step 7

Measure a hackle feather on a hackle gauge a size or two larger than the hook size. Orientate the feather so the backside of the feather, or dull side is facing you. Strip the fibers to expose roughly a 1/4” of the stem, and additionally remove a few more from the left side. This allows the hackle wraps to have a clean, neat start. Tie the stem on the near side of the post at a 45° angle, allowing most of the stem to clear the post height. Take a gentle wrap or two around the base of the post to start binding the hackle stem to the post. Grab the hackle and move it to the right side of the post, so that the more stripped side of the hackle is touching the post. Wrap your thread up the post, securing the rest of the stem, and take flat open wraps back down until you’re back behind the post and onto the shank again.

Step 8

Blend the SLF squirrel dubbing with the Kapok dubbing by stacking two small amounts on top of each other, and begin tearing the bundle apart. Re-stack the two bundles and repeat this a number of times until the two are married. The Kapok gives extra floatation, and the rough, spikey squirrel dubbing gives the illusion of legs. Create a tapered dubbing noodle and begin building a bulbous thorax, covering the shank behind and in front of the post. It helps to not overtighten your dubbing, as the coarser appearance gives a more buggy, lifelike appearance. Finish just behind the hook eye with bare thread, ensuring no dubbing is too close to the hook eye. This also ensures a clean finish.

Step 9

Take your hackle and begin taking counterclockwise wraps down the hook shank. Remember, the first wrap is the most important wrap. Like a Domino effect, it will dictate how the rest of the hackle will land, so make sure this is oriented well. It’s never a bad thing to take your time setting up, and reversing if it doesn’t look right. 5-6 wraps should be just about enough. On the last wrap, finish with your hackle stem just behind and to the far side of the hook eye. Holding firmly in one hand, cross your thread over the hackle tag 2-3 times before increasing your thread pressure and securing the hackle stem. Lift the hackle stem and cut as close as possible to remove it. Take a few more wraps to ensure it is bound down well. I recommend using half hitches to finish this, as it can get into tighter spaces like this without trapping any hackle fibers. Add 3 half hitches to finish and cut your thread. This is where you can clean up any remaining unruly fibers with your scissors. Use Solarez Bone Dry to saturate your finishing wraps and fire with a UV light.