Spruce Moths & Tricos – Late summer flyfishing bounty

Paul Vang’s Spruce Moth

We spent the last couple weekends of July camping on the Big Hole River, and while walking around the campground I saw little, white moths fluttering around the shrubbery.

Then it hit me. Spruce moths!

As we go through the fishing season we mark the passage of time by insect hatches, tracking time by skwalas, blue wing olives, salmonflies, golden stones, pale morning duns, and now in August we’ll note the new page on the calendar with spruce moths and tricos.

Up until now, most of the fly-fishing action has centered on imitating aquatic insects, such as the various mayflies and stoneflies. With the spruce moth, we have the first major invasion of terrestrial insects on our trout waters, and the fish will be paying attention.

I remember an outing last year when I spent the morning fly-fishing with tiny trico imitations, catching mostly whitefish. Around noon, the trico action petered out, but after a sandwich break I went a short distance upstream and noticed fish rising along a current seam. That caught my attention and I checked it out and trout were rising to the all-you-can-eat buffet of spruce moths drifting helplessly along the water’s surface.

For the next couple hours I had continuous action as I worked that current seam up the river, catching and releasing a number of trout that fell for my fake moth.

The spruce moth is the adult form of the western spruce budworm, an insect that feeds on Douglas firs, spruce and also lodgepole pine. A Forest Service bulletin describes the spruce budworm as a “defoliator,” as the mature budworm larvae feeds on needles or needle buds. Trees that have been damaged by spruce budworms may be more susceptible to other parasites, such as bark beetles.

It’s the adult form of the budworm that gets the attention of trout and trout anglers. The adult moths emerge in late July and August. The moths lay eggs on the underside of conifer needles. The eggs hatch in about ten days, and the young larvae spend the winter in a silken casing called a hibernaculum. They do most of their feeding on host trees in May and June, before morphing into the adult form and repeating the process.

While I started seeing spruce moths in mid-July, I wasn’t seeing them on the water. It seems to take a little while for the explosion of adult moths to reach a critical mass when the moths seemingly start to migrate to water and, inevitably, become fish food.

Bob Jacklin’s Spruce Moth

There are many fly patterns designed to imitate the spruce moth, starting with a basic Elk Hair Caddis. I just tied up several, though with some variation. The spruce moth floating down the river is splayed out, flat on the water’s surface. I tied the fly with the palmered hackle clipped flat on both top and bottom of the hook, and the elk hair wing flattened out. I also tied them on a #14 dry fly hook. Some recipes call for them to be tied on a #12 or even #10 hook and that seems way too big as an imitation. Of course, the ultimate judge is the trout, not the angler.

Now, a note on tricos. Trico is short for Tricorythodes, a tiny mayfly that emerges into adult form starting about now, and going well into September. The bug is small, but they emerge in incredible numbers and return to make egg-laying flights over the water in clouds of bugs. Considering the millions of mayflies in one of those clouds, and the numbers of those trico clouds over the miles of river, the numbers of insects is mind-boggling.

Trico hatch on the Big Hole River.

And, again, the fish take notice. There’s not much protein in the individual bug, but it adds up, and the fish get busy.

Keep in mind; fishing the trico hatch is a morning game during these hot, summer days. The action runs from mid-morning to around noon and then it’s done for another day.

But, you might still get spruce moth action. It’s all good.

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