Male Tricos hatch the evening before, typically between 6 p.m. and dark. Anglers will fool a few trout with dun imitations, but the main emphasis of the Trico hatch should be placed on the morning spinner fall.
Spent-wing Tricos have a distinct silhouette that distinguishes their appearance from the duns. Spinners lie on the water spread-eagle, with the tail, abdomen, and wings sitting flush on the water. Anglers who fail to switch from upright-wing dun imitations to spent-wing patterns will most likely become frustrated quickly from their inability to catch fish. Unlike duns that leave the water quickly, dying spinners remain on the water for long periods of time. Trout recognize this opportunity and feed on them with a vengeance. My favorite Trico imitation is Shane Stalcup’s CDC Trico Comparadun. It fishes well for both Trico duns and spinners and can be fished as a drown spinner by simply adding a #6 split shot and fishing it mid-column.
Towards the latter part of September, the Trico hatch takes on a new twist as the males no longer hatch in the evening due to cooler air temperatures. Cool mornings have the same affect on the females too, which delays the hatch an hour or two. The two hatches (the males which normally hatch in the evening and the females that hatch in the morning) involve into one, with the male duns hatching first, followed by the females. Spinner falls typically occur around noon and last for an hour or so. The most reliable Trico hatches are found in Elevenmile, Cheesman Canyon, Deckers, Arkansas (Pueblo tailwater), Yampa, Gunnsion, Colorado, and Williams Fork.