There are many methods used to split tails on dry flies. If you fish a lot of spring creeks or flat water sections of rivers, as I do, you tend to wind up using lots of comparaduns, no-hackles, spinners, thorax flies, and even some parachutes with split tails. The method I'm showing here is not recommended for no-hackles, though I've used it for them, but works particularly well for any fly with biot or quill bodies. As a devote of A.K. Best I can vouch for quill bodies, and will fish them whenever possible over flies with dubbed bodies. When splitting tails on those flies, I don't like the dubbing ball method as I don't see many mayflies with a big dubbing ball on their rear end. In the case of the no-hackle fly however, the dubbing is an absolute necessity for floating the fly, and in that case I would use a dubbing ball rather than the thread ball shown below. For quill body comparaduns, thorax flies, and spinners, the thorax is dubbed, so floatation is less of an issue. I like a 90 degree spread on the split tails, if I can get it, as it adds a lot of stability to the fly in the water. For that reason, I use microfibbets for tailing material on many of these flies, as I can achieve that spread more easily. Hackle is great too, and I use hackle for tails on most of my no-hackles these days, three barbs on a side. Many feel that fish like hackle better, that they are put off by the feel of microfibbets. I've used both, and had good results either way.

The method I show below is an amalgam of a couple of tried and true ways of splitting tails, with my own wrinkle. Thread torque is always your enemy in tying flies, and no more so than when it comes to splitting tails. The near tails will always tend to rise up, the far tails will tend to get pulled down, as you wind the thread. With the method shown you will stabilize the near tails early in the process, so all you will then need to worry about are the far tails, and that's the beauty of it.

Wind your thread starting at the eye, back to the tail tie in point, leaving a tag end of two or three inches. This tag will be used to split the tails.

Build a small thread ball with 6 wraps or so of thread, wrapping in a "X" fashion. It helps to hold the tag end up at an angle, under tension, as you wrap against it.

Now wind the thread forward with four or five spaced wraps, to around the thorax position on the fly.

After measuring your tails against the hook shank, tie the bundle in on top of the hook at the thorax position, while holding the bundle against the thread bump. I like to roll the bundle to the top of the hook, using thread torque to pull it up there. Then, after securing with a couple of thread wraps, I'll adjust the bundle with both hands, making sure it's right on top.

Next, wind the thread back halfway to the thread bump, holding the tailing fibers in place, as shown above.

Now bring the tag end of the thread up between the microfibbets or hackle, splitting the bunch exactly in two. You can use your left hand to fan them, then use the thread to split them. If there is a hard part, this is probably it.

This is where my method deviates just a little from ones I've read about. Here I'm holding the tag end with my right hand, angled down, under tension, on my side of the hook, in such a manner as to force the near tails into the thread ball, about halfway down the ball. In other words, I'm going to use the tag end of the thread to insure that the near tails won't ride up as I wind the thread further. I'll secure the tag end on my side of the hook with a couple of hard wraps using my left hand, and then continue wrapping with my right once the near tails are secure, toward the thread ball.

Here is the fly shown just after securing the tag end with two hard wraps.

Now I'm wrapping back to the thread ball, holding the far tail in place, forcing the tails against the ball as I wrap, splitting them

At this point I've wrapped all the way to the thread ball, holding the far tail in place with my left hand, and the tails are now split.

Here is a top view of the split tails. Notice the 90 degree split. And finally, a spinner tied using this technique.