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 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 F.

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 mid-October, 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 daybreak 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.

The positive aspect, ironically, is the Trico's size. Tricos are generally size 20 to 26, which means it takes a large number of these little morsels to make a meal. Therefore, trout rise repetitively. This gives you ample opportunities to get your drift right and hook up.