The Trouble with Tricos

The Trouble with Tricos

They’re too small. They’re too numerous. And because trout go bonkers for the miniature mayflies, they’re too hard for any fly angler to ignore. By Tom Dickson.

This story is featured in Montana Outdoors July–August 2015 issue

My best and worst episodes of trout fishing in recent years came during Trico hatches. The best came late one mid-October morning on a channel of the Bighorn River, when my friend Rob and I caught 20 to 25 browns between us in an hour. We hadn’t expected such great dry fly action so late in the year, and by the time the Trico hatch and spinner fall were done, we’d collapsed on the bank, stunned and smiling at the wonder of what had just happened.

The worst was a morning last August on the Missouri, when I stood in a channel upstream from Craig surrounded by at least 20 big rainbows rising to Trico spinners. I tried every Trico pattern in my fly box and varied every possible way to deliver those flies to the fish. After two hours in the hot late-summer sun without a single take, during which the trout never stopped feeding, I reeled in and trudged back to the parking area, a beaten man.

That Tricos can create such angling highs and lows is not surprising when you know a bit about these tiny but remarkably abundant mayflies. Their small size, great abundance, and hatches that go on for months make them one of the most anticipated and frustrating insects on Montana trout rivers.

Biology lesson
To catch trout during a Trico hatch, it’s worth knowing a little biology. The Tricorythodes family of aquatic insects is a type of mayfly, related to Baetis (Blue-Winged Olives), Pale Morning Duns, and the others that live in Montana rivers and coat your windshield during warmer months. Like midges—which they resemble but are only slightly related to—Tricos live in silty river bottoms and are most abundant in slow-moving waters like below dams or in the tailouts of deep, slow pools of freestone rivers. Every major Montana trout river grows Tricos. Hatches are most prolific and long running on the Missouri below Holter Dam and the Bighorn below Yellowtail Dam. The Bitterroot, Big Hole, Clark Fork, Yellowstone, and Beaverhead also produce prodigious hatches, though not lasting as long.

Tricos hatch as early as July and as late as November, depending on river and air temperatures. Male Tricos emerge first, late at night or just before dawn, transforming from underwater nymphs into winged sexually immature adults known as duns. The insects float on the water surface like tiny sailboats for several minutes, drying their newly emerged wings before they can fly off. The males land on shore, molt again—this time into the sexually mature phase known as the spinner—and wait. Females emerge on hot mornings as early as dawn and on cooler mornings as late as noon.

After the females have molted on land into spinner form, both sexes take flight and gather in massive swarms over the river to mate. From a distance, the swarms resemble clouds of dust, often rising 50 or more feet above the water surface. After mating, the male spinners fall to the water surface in the “spent” position—wings outstretched on each side. The females fly to shore to rest for a bit before returning to the water to drop their eggs, after which they too drop dead onto the water surface.
During the spinner “fall”—which happens at about 9 a.m. in August to around noon by October—the water surface can be covered with millions of spent Trico spinners. So abundant are the mayflies that it’s worth a trout’s time to eat the tiny offerings. The fish set up in feeding lanes in slow current and steadily rise to the conveyor belt of food moving overhead. Trout feeding on Tricos often fall into a rhythm, rising meth­odically every five to ten seconds. The steady pattern likely allows the fish to use as little energy as possible.

The bigger trout often hang out near the bank, where the current is slowest. Those flat slicks are one of the hardest places to catch trout. Errors like a dragged fly or shadows caused by errant casts, elsewhere hidden by broken water or current, cause shallow-water fish to spook and dash to deeper water.

How to connect
When mayflies cover the water surface, a trout doesn’t need to move more than a few inches to feed. That means your fly has to drift right over its nose. And if the fly isn’t in the prime spot when a trout happens to be rising according to its established rhythm, the offering may be ignored. Even the best anglers sometimes make a dozen or more perfect drifts with the perfect imitation before the trout happens to rise and open its mouth at just the right moment.

Early in the morning, your best bet is to throw dun patterns (upturned wings) imitating newly emerging females. After the spinner fall, the best patterns tend to be spinner imitations, with wings extending out perpendicular to the body. Female duns and spinners have a cream or pale green body, while the male’s body is black. Most spinner patterns have poly or Antron wings that help keep the fly from getting waterlogged. Oddly enough, fly shops also sell “drowned spinner” patterns that represent the insects as they sink below the surface.

Most anglers try to match the exact size of the Tricos they see on the water, which can be anywhere from a minuscule size 24 up to a relatively large (for a Trico) size 18. They reason that the trout are so focused on the Tricos floating overhead that they will ignore anything that deviates even by a fraction of a millimeter.

Yet other anglers swear by larger imitations, arguing that with so many similar-sized naturals on the water, it takes something different to catch a trout’s attention. Another advantage of bigger patterns is that they are easier to see. Older anglers especially gravitate toward a more visible double spinner pattern or even a “cluster,” which resembles several dead Tricos stuck to each other on the water surface.

I usually go big and small—a size 16 Griffith’s Gnat or Parachute Adams with a size 20 Trico spinner as the second fly tied about 12 inches behind. The big fly, which trout occasionally take, gives me some sense of where the other, near-invisible fly is drifting.

Then there’s Mike, an older friend of mine who fishes only a size 12 Parachute Adams on the Missouri and regularly hooks fish rising to itsy-bitsy Tricos.

Look closely at the Tricos floating past. Last September I cast fruitlessly for a half hour to several trout rising to spinners before noticing that the flies on the water were mostly females. I switched my black-bodied size 18 spinner for one with a cream abdomen and hooked a trout on my next cast (though I didn’t catch another fish the rest of that morning).

Slow and stealthy
The spinner fall in late summer is usually over by midmorning, but you can still use Trico patterns well into early afternoon. Trout continue to rise to dead spinners as they float downstream for several hours after the main action upstream has finished.

Because the best Trico fishing comes on hazy sunny days, you have to be especially stealthy. Save the bright cap and shirt for the beach. Trout can see colors and will spook from gaudy attire. The best angler I know dresses pretty much the same for trout fishing as he does for bowhunting. Also, don’t false cast over rising fish, which sends a shadow that often makes them quit feeding. Even if they continue sipping the surface, the fish are aware of your presence and will ignore anything that isn’t a bona fide natural.

Use a long leader (12 feet) and thin tippet (3 feet of 6X) unless the wind or your casting ability requires shortening up. Many successful anglers grease their tippet with floatant up to within 6 inches of the fly. That keeps the tippet riding high on the water surface where it will be less affected by currents that cause microdrag and move the fly unnaturally.

Watch guides on the Missouri, Bighorn, and other classic Trico waters, and you’ll see that they position their boats so clients can cast to risers from far upstream of the fish. The trick is to cast down and slightly across, adding an aerial upstream mend or wiggle cast to get lots of slack in the line to counteract all the complex currents on the water surface. Shake out fly line from the rod tip to help get a drag-free drift. The benefit of casting downstream to trout is that they see the fly before the tippet and leader. The disadvantage is that it’s tough to get a good hook set. Too quick a set and you’ll either pull the fly out of the fish’s mouth or hook only its hard upper “lip,” from which the hook can easily pop free. To firmly stick the corner of the jaw, pause two seconds after the take so the fish has time to turn slightly before you set the hook. Another challenge is that with 15 feet of leader and tippet plus 30-plus feet of fly line on the water, it can be tough to set the hook before a trout spits out the imitation.

If that happens, console yourself that at least the trout took your fly. During the mesmerizing-but-aggravating Trico hatch, that in itself can be considered a victory.Bear bullet


Tom Dickson is editor of Montana Outdoors.