If you’ve been fortunate enough to be on a Montana trout stream during a major insect hatch, you know how good the fishing can be. Anglers try - often in vain - to time their fishing trips to coincide with a prolific hatch.

During any hatch there exists a critical moment - the transitional period when an insect breaks free of the underwater world and becomes an adult. At that moment, the insect emerges from its nymphal shuck, dries its wings and flies away … unless, of course, a trout eats it.

Fly tyer Gary Jones of Bozeman has developed a new line of flies intended to mimic this transitional phase of the insect. He calls his flies Emergaduns.

“(Insects’) wings are all crumpled up as nymphs and when they emerge those wings sprout through the surface,” Jones said Tuesday. “That emergence is what the Emergadun represents. It is an emerger becoming a dun.

“Of course a lot of this is of the imagination of the fly tyer,” Jones said. “You wonder what it takes to outsmart a trout, when they have a brain the size of a pea.”

Jones’ Emergadun patterns are similar to the Klinkhammer flies developed by European fly tyer Hans van Klinken. The Emergadun - like the Klinkhammer - is designed to rest half above the surface of the water and half below.

Matching the emerging stage of the insect is essential to the Emergadun’s success. Jones said trout might take the Emergadun as an emerger, a dun or a cripple.

“There are many good flies that sit below the water and above the water, but that transition to a dun is when the fly is most vulnerable,” Jones said. “They can’t get away until their wings are dry enough to fly. That is when fish most like to feed on them.”

Jones said the Emergadun pattern capitalizes on what he calls “trigger points.”

“When a fly tyer works toward a new fly, we try to work in as many trigger points as reasonable,” Jones said. “Probably the most popular fly is the Elk Hair Caddis. Those little tips of the hackle create prisms under water. If you look at it from underneath, it glows. (The Emergadun) also glows.

“Another trigger is that it penetrates the surface film,” Jones said. “The trout can see it in his world. That is why the penetration of the surface is so important.”

The Emergadun is tied with just a few materials chosen specifically for their ability to suspend the fly in the surface film. The fly uses Antron for a trailing shuck, which naturally sinks. A turkey biot is used to create the ribbed body of the fly. Finally, the fly is topped with several wraps of oversized hackle tied parachute style and a polypropylene post for maximum buoyancy.

Tied on hooks from size 22 to size 10, the Emergadun can be fished to mimic the emerging state of a broad array of insects. Jones said that with a simple variation in color everything from midges to green drakes can be matched with the Emergadun.

Jones, who has fished in and around Gallatin Valley for the better part of 50 years, will begin teaching adult education fly tying classes next week. The classes will be held at Monforton School and Gallatin Gateway School.

Don Schmidt, of Gallatin Gateway, said Jones’ patience and passion for fly-fishing make him a great angler and fly tying instructor.

“Gary is probably the best fly fisherman I know,” Schmidt said. “He has the patience, the technique and he catches a lot of fish. He takes time to listen to you and lets you ask questions, and he has great stories to tell you while you’re tying flies.

“I think tying a fly is somewhat of an art,” Schmidt said. “Gary is head and shoulders above others in his art skills.”

Schmidt said he took the class to learn to tie his own flies. A high mountain lake angler, Schmidt said he’s taken several fish on woolly buggers of his own creation.

Jones said he’ll share his Emergadun pattern with interested students, but the fly can be a bit of a challenge for beginning tyers. He said the fly works well throughout the season, and even works as an attractor pattern when bugs aren’t hatching.

“The Emergadun is simply an emerger becoming a dun,” Jones said. “It is a combination of those two things. And it catches lots of fish.”

Ben Pierce can be reached at bpierce@dailychronicle.com and 582-2625.