Tricos: Conquering Wyoming's "White Nightmare"

This hatch happens every morning from June until mid-October–five straight months of nonstop action.

September 02, 2024 By John Schwalbe

This article originally appeared in the September 2008 issue of Fly Fisherman.

I have several conversations through the year that begin with someone asking, "When is the best time to visit Thermopolis, Wyoming, to fish the Bighorn?"

My reply is generally the same: "For the best chance at rising trout, get here in June for the Tricos."

"Tricos in June?" they say.

Then I explain that this hatch happens every morning from June until mid-October–five straight months of nonstop action. This leads into extensive dissertations about this abundant hatch, which has come to be dubbed "the white nightmare" or "white-winged curse" because of its ability to drive capable anglers into rod snapping fits of frustration and rage.

Here on the Bighorn, and on similar Trico factories across the country, these diminutive (#20-26) and profuse mayflies get browns, cutthroat, and rainbow trout feeding more frantically than most other annual insect emergences. Conquering the white nightmare, however, is another story.

The head of a rainbow trout half in the water. — (Barry & Cathy Beck photo)

The Hatch

Tricorythodes is the fancy latin genus name of the mayflies better known as Tricos. In the West, they usually start their emergence near the end of July. On the Wyoming Bighorn, however, the hatch usually starts in early June when water temperatures reach 62 degrees E Thermopolis is in a high-plains desert area, so things warm up quickly, and Boysen Dam releases water into the river from the top of Boysen Reservoir where the water is warmest.

Early in June and again in September through midOctober, Tricos offer a large window of opportunity to cast drys to rising trout. That window gets smaller on the Wyoming Bighorn as the heat gets more intense. Trout still surface regularly through the dog days of summer, but only for a few hours in the early mornings. Male Tricos hatch at night and molt into spinners in the bank foliage. They have black or dark brown bodies and clear wings. At daybreak, the olive-bodied females often mistaken for Blue-winged Olives-emerge as duns.

When fishing this early morning hatch it sometimes helps to use olive-bodied flies to imitate the females.

The female Tricos fly to streamside foliage-where they molt into spinners-and then they join the males later in the morning in large mating swarms above the riffles. These mayfly clusters can be so dense they look like fog or smoke in the morning air.

The spinner fall seems largely dependent on air temperatures between 65 and 70 degrees. In June, July, and August this can be early in the morning, often between 7 and 8 A.M., but it can also appear a few minutes after day break or in the fall as late as noon.

After their mating ritual, Trico spinners fall dead with spent or outstretched wings flush with the water’s surface. This stage—which usually results in carpets of bugs on the surface—gets the most attention from trout. This is also the phase that gives most anglers frustration because it is less about pattern selection and more about precision and accuracy. These trout typically won’t move to take a fly, and you’re better off using a force-feed approach, casting to within inches of their vacuum swirls. Why would a trout go out of its way to take your fly—made of feathers and synthetic materials—over the surplus of naturals already available on the water? This is the drawback of this hatch.

Trout are not comfortable feeding on the surface, which is why they predominantly feed below it. When they are on top, trout are more vulnerable to predators. When they group up, they lose their territorial behavior, and take advantage of the “safety in numbers” principle. If one of them senses danger, they often all react to it.

Frequently, the fish feeding at the top or front of the pod is the largest or most aggressive. But if you approach from below and cast to the lead trout, your line is likely to spook the entire pod. If you approach from above and across, you might be able to present your fly without spooking the trout, but your first fish might also be your last, as the group is likely to spook from the splashing.

By approaching from below and targeting the back of the pack first, you can pull individual fish out without disturbing the others. Be careful to present the fly only about a foot in front of the rear or outside fish. In this case, it’s better to cast short and gradually increase your distance than to throw a long bomb into the middle of the pack.

A trico mayfly on a late-summer weed. — (Barry & Cathy Beck photo)

Trout in pods feed with relative consistency—allowing you to time your casts to coincide with a pending rise. The other way you see trout rise is when they cruise the surface in the same general area—disappearing and showing in a slightly different place or direction. Some- times a pattern develops: for instance, a trout may rise three times, go down, cruise upstream a few feet, and rise again three times. If it is a true pattern, then anticipating the next rise allows you to place your fly accordingly.

Unfortunately, sometimes there is no rhyme or reason to when or where the next rise happens. In this case, your only options are to pepper the area with casts or look for new fish.

Trico Tactics

I have had clients in my boat who doubted both my logic and the flies that I tied on their lines. It’s not uncommon for the fly to pass directly over a trout with no strike. This is due to the number of insects on the water’s surface. The trout rarely pick out individual insects. Instead, they use the current to move rhythmically up and down, gorging in the most efficient manner possible.

If you are not getting hook-ups, it is usually because of one of three things: timing, accuracy, and presentation. These are the most important factors during this hatch— even more so than the fly pattern.

Basic mayfly combinations, such as an Adams with a Trico spinner dropper, will catch any fish eating Tricos. However, your timing must be precise. That means luck has a lot to do with it, as well as the law of averages.

Instead of bunch-shooting into the pod, you must land your flies in front of a specific trout as many times as possible. As soon as your flies go over the trout, let them drift past the fish before you pick up, so you don’t spook it. Get the flies in front of the same fish again and again. Excessive false-casting wastes time and decreases the odds of the fish taking your fly. Keep your fly on the water.

The second factor is accuracy. These fish do not need to move to the left or right to get your fly. Why should they? There are thousands of spent Tricos floating right to them. All they need to do is tip up, open their mouths, and dip down. Your fly must drift exactly over the trout as many times as possible.

To improve exposure, cast only about 12 inches upstream of the trout. A long drift is not required, and long drifts can actually thwart your efforts if the current draws the fly to one side or the other.

A large brown trout held just above the water's surface. — In pod feeding scenarios typical with Trico hatches, the fish feeding at the top or front of the group is usually the largest or most aggressive. If you approach from above and across, you might be able to present your fly without spooking the trout, but your first fish can also be your last. (Barry & Cathy Beck photo)

Also, get as close as possible to the fish. Use stealth, and crouch and kneel if you must. This is critical because if you are 15 feet away you can put the fly on the button more consistently than from 40 or 50 feet.

Presentation is the final important consideration. A dragging fly may get smaller fish excited enough to chase it, but you will not catch many large trout. Watch the real Tricos on the water while you are drifting your flies. Your flies should drift at exactly the same speed as the other floating insects.

As stated, short drifts directly over the fish are normally best. If you must make a long drift, a reach cast can help— especially if there is fast water between you and the trout. Reach upstream on your forward cast so the fly line lands upstream of your flies. As the current removes this upstream bow in your line, your flies will drift freely without dragging. Another technique is to cast at a sharp downstream angle and feed line and your fly directly toward the rising trout. This extends your drift, which could make the difference in getting it over the fish. Unfortunately, the more line you have out, the harder it is to set the hook when your fly is eaten.

For Tricos, use 9- or 12-foot tapered leaders with 2 to 3 feet of 5X or 6X tippet. Some experts advocate longer leaders but they are harder to cast accurately. I like fluorocarbon for its strength and light-refracting qualities. This helps when trout are feeding in slower water—with fewer bugs on the surface. These fish have ample time to examine your flies, and often spook if they see your leader and tippet first.

In pod situations, use indicator flies such as a Sprout Trico, Pablo’s Cripple Tridge, or a high-vis CDC Compara-dun Trico. These flies are easy to see, especially on long casts. If you cannot see your fly, you’ll never know if you are casting accurately.

When spinners blanket the water, attach a spinner dropper 12 to 14 inches below a dun pattern. I know a lot of guys want to cast only one fly. However, you will put more fish down by “guess setting” rather than actually seeing your flies eaten. I usually dress the spinner pattern to keep it floating for risers.

In the late morning when the spinner fall is winding down, I tie a sinking spinner below my dun pattern to get a foot or two under the surface. The most realistic pattern I know is the Evetts Spinner. Spent Tricos naturally start to sink after time, and trout key in on them. I even use a spinner as a nymph tied below a Pheasant Tail after most of the fish are down for the day.

I prefer 8 1/2-foot 4-weights with weight-forward floating lines for casting drys on the Bighorn. Use a 9-foot 5- or 6- weight rod for bigger waters and windy conditions. Also, it is important that your line color is not too bright. Muted olive is less noticeable to the fish.

Boat Fishing

The best way to fish many Western rivers—particularly during a Trico hatch—is to float them. You will cover more territory and find more pods of fish this way. Drift boats can also give you a better vantage point and control of your fly line.

When drifting in a boat, scan constantly for rising trout. This is sometimes obvious, like a large snout opening wide and breaking the water, or better yet, a group of large snouts.

A splashy rise usually indicates a smaller fish, but subtle dimples can mean a large trout is sucking down spinners from just below the surface. After you know what to look for, you will spot fish more frequently.

When I see a good trout surfacing, I slow the boat with a hard backstroke. I leave the oars deep in the water for leverage, and ease in as close as possible. I lean toward the conservative side, because I would rather make longer casts and keep the fish feeding than get too close with the boat and put them down.

With beginners, it is better to work on improving their casts then to attempt getting too close. I also stay upstream of the trout whenever possible. This helps you get your line upstream of the flies and achieve better drifts.

Using this boat position, pick off the outside fish first, and gradually work your way to the inside of the pod. When you approach a pod on foot from below, you naturally get better hooks-sets, because the hook is drawn into the fish’s mouth when you raise the rod. When approaching from below, you can also get closer to the trout.

Be aware that in a boat—from an upstream position—you will have to make longer casts. When you set the hook, sweep the rod down and to the side to improve your chances. Even then, with a small hook, you will miss some trout.

When the boat is in position, ease the anchor down. I’ve seen guys just step on their releases and let their anchors splash into the river. Then they wonder where the fish went. Instead, push the release down with your foot while holding the rope, and gently lower the anchor into the water. Let out enough rope so the anchor is angled adequately to hold you steady.

While anchored you can use your oars to maneuver the angler standing in the bow of the boat closer to the fish. If the trout is feeding on river left, turn that same-side oar sideways so it lies flat on the river surface. Then turn your right-side oar perpendicular to the water where it pushes against the current and sways the angler closer to the fish. You can also push against the current with the oar to gain more distance. Every little bit helps.

Sweet Dreams

Even though Tricos can be difficult, they provide great opportunities for nice trout on drys. The Trico hatch on the Bighorn is so prolific it’s developed a cult following similar to Salmonfly hatches on other rivers—except instead of casting a #8 fly on 2X tippet, you’re casting a #18 on 5X. This takes delicate casts, hook-sets, and fighting. But the rewards are worth the challenge: boiling water, bobbing heads, cruising pigs, and the hatch also known as the white nightmare.

The West’s 10 Best

Tricos are a go-to summer staple on many tailwaters throughout the West. The following are FFM’s top picks for chasing the mini black-bodied mayflies and the slurping heads that pursue them.