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The Trico

by Jon Easdon, Director of Services

Trico mayfly


It’s that time of the year that all fly fishers look forward to. The time when we squint our eyes and frantically throw size 24 dry flies to rising trout. The Trico (pronounced TREE-co, often mispronounced as TRY-co) is a small mayfly prevalent from about mid-July to late September. Tricos are small, ranging from 3-7 millimeters in length. They become a staple on most every cold river in the west. On the South Platte, the Trico turns into the preferred meal of trout. These hatches can be so intense that their swarms look like smoke above the river. Because of the density of these hatches, they tend to lure all of the trout to the top of the feeding column on the river.

a “cloud of Tricos” during the morning hatch

(photo: Dave Herber)

Tricos prefer cold water and silty, weedy areas in deeper pools on the river. The hatches are fairly predictable, with water and air temperature being the key to the hatch. The morning to mid-morning is typically the best time to witness these hatches. This is followed by the “spinner fall” when most of the feeding occurs. The Tricos fall mercilessly to the surface of the river kicking off a massive feeding frenzy.

Fishing this hatch can be notoriously tough. The fish really seem to key in on certain sizes and life stages of these mayflies. Over the years, on occasion I have personally thrown a bunch of different patterns trying to fool the fish to no avail. Studying the fish and their behavior is important in fishing this hatch. You can time the rises and time your presentation. Take the time to watch the fish before you go hucking flies at them. A little patience can pay huge dividends. I would also suggest having a second rod already rigged with a dry fly/ dry-dropper system. These hatches can turn on and off like the flick of a light switch.

Here are a few techniques and patterns I like to use during the Trico hatch.

Before the hatch really begins, a standard nymph rig with a black RS2 (size 22-24) will produce success. Green RS2’s can also be electric as they signify the female Trico. In my opinion, the RS2 should always be a staple in your fly box. I also like to fish small zebra midges during this stage.

Black RS2 emergers or a black baetis emerger will signify the emergence stage. The density of these mayflies keeps these nymph patterns valid all day long as well.

During the spinner fall, I like to throw a combination of adult Trico dry flies with a spent -wing dropper. A very important thing to look for during the spinner fall: refusals to your flies. If you get a couple of refusals, change your flies! It’s worth the time because when you do discover the hot pattern, you can hook up on almost every cast.

Here are some of my go to patterns for the Trico’s:


  • Black RS2 (size 22-24)
  • RS2 emerger-whitleys sparkle wing (22-24)
  • Mayhem size 22
  • wd40, black, size 22

Adult dries

  • Juan’s 180 degree trico (24)
  • Neil’s smokejumper size 22
  • vis a dun, black, size 22

Spent wings

Engle’s drowned trico (pictured; 22-24)

Mayer’s tails up trice-size 20, 22

Poly spinner (22-both male and female)

I hope you can get out and enjoy one of the most fun dry events of the year. The Trico hatch can be extremely rewarding when you take the time to figure it out. Please stop by the shop and we would be happy to show you these patterns or just talk Trico’s.

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