trico dun by umpqua copy

trico dun by umpqua copyGuest Blogger: Joe Dellaria

The first time I saw a Trico spinner fall was mid-July. The good news was, I had read an article and was able to recognize what was going on. The bad news was, I didn’t have any trico spinner flies and watched helplessly while standing in the middle of a trout feeding frenzy. I did manage to entice one nice trout to take a grasshopper. That was a consolation prize as I watched dozens of fish feeding with total abandon within four or five rod lengths. At one point, the spinner fall was so thick, a 20+ inch trout simply opened its mouth and mowed a strip of tricos down the hatch as it swam across the run.

Once again, my lightning quick mind concluded, “Hey, I better learn how to do this.” So, the aim of this article is to arm those who are new to, or have little experience with, the Trico spinner fall so they can join the fun. This is an amazing opportunity for some excellent fly-fishing from early- to mid-July into fall. It definitely requires technical fishing skills, but with a little knowledge and persistence, it can become a steady source of many fish on the end of your line.

The Trico, or Tricorythodes, is a small, actually, very small mayfly that trout absolutely love. The reason is obviously not size of the mayfly it varies between 3-6 mm (3/16” – 5/16”) in length. Trout love the trico because it has a spinner fall that lasts anywhere from a half hour to an hour and a half long. For those in the know, you can easily add an hour of excellent fishing on either end of the spinner fall.

What I would like to share are the basics that will allow anyone to take advantage of the Trico spinner fall. The table below provides the basics of how to fish the Trico spinner fall:

What Happens What I do
1 Males hatch at night. Nothing, get more sleep. It’s hard enough to hook a trout on a #18-#22 hook when you can see it. At night, it’s virtually impossible (at least for me).
2 When the air temperature reaches around 65 degrees, females begin to hatch. Some trout will feed on the hatching females. Use a two-fly rig with #16 Parachute Adams or BWO with a #16 beadhead Pheasant Tail or Prince (or your favorite local pattern)
3 Eventually the males and females meet in the air to mate. In a good year, you can visibly see mating swarms in balls several feet in diameter. This means the spinner fall will start within an hour or less. Keep fishing the two-fly rig. Eventually, the fish will stop taking either fly. It will be very obvious. When that happens, switch out the nymph dropper, for a male trico spinner. I start with 5x tippet on the dropper. If I get two or more refusals, I drop to 6x. Still more refusals, drop to 7x.
4 After mating, the male duns will molt and drop as spinners on the water first. Fish will set up in feeding lanes. Now the fun begins. Start casting to the most downstream and closest fish to your side of the stream. You need to time your cast to the fish’s rises so your fly is floating by when it is about time for the fish to take again. Keep casting to that fish until you either hook it, or it stops rising. Cast to the next fish across the stream until you either hook it, or it stops rising. Once you work across the stream and run out of fish, take a few steps upstream and repeat the above process. 
5 The females will deposit their eggs, molt, and fall as spinners after the males. At times both males and females can be on the water at the same time. Some people claim they have never seen trout be selective between males (black body, black abdomen) and females (white or pale green body, black abdomen). I find the trout to be selective on my streams. If the trout are selective, you will stop getting takes on the male trico fly. Switch to the female
6 For the first week or two of the trico spinner fall, the fish feed voraciously (If you clean a fish their intestines and stomach will look like and over-stuffed sausage). As one of my friends puts it, “The fish get rock stupid dumb!” During this time, you may be able to catch several fish out of a heavily feeding pod of fish. You can drag a hooked trout right through the middle of the feeding frenzy with no apparent effect. As the season progresses, fish will get more wary. Picking off the most downstream fish will become increasingly necessary if you want to catch more fish.
7 Eventually there are very few spinners on the water. There are always a few diehards looking for the last morsel. You can still pick these fish off but your approach must be increasingly stealthy and small casting errors will often put the fish down.
8 Fish will stop rising completely. Bummer, but not to worry. You can switch out your floating spinner fly for a drowned trico pattern and dead drift it through riffles and other areas where you were catching fish earlier for up to 2 hours (so they say). I find this to be effective for 30 minutes and sometimes for an hour.

It’s Air Temperature Not Time of Day: Many people want to know what time they need to be on the water. The spinner fall is driven by air temperature. In July and August, the evening low might be in the mid-70s. When that happens, you may catch the tail end of the spinner fall if you show up at sun up. In late August and September, the air temperature usually reaches 65 between 9-11 a.m. Later in the season, it could be later. This year, we had a cold snap in August and I saw my first trico spinner fall in the evening!

Stealth Become Increasingly Important As The Season Progresses: Initially the trout are ravenous during the first week or two. In addition, the fishing pressure will steadily increase as the word gets out the trico fall is on. Consequently, the fish get pickier on the fly pattern and less forgiving on sloppy casting and noisy approaches.

Break-offs Are Inevitable: If you are lucky, you can get by with a 5x tippet, especially during the first week or two of the spinner fall. Eventually you will have to drop to 6x to get takes. If the water is very clear and slow, 7x may be necessary. The fish know how to break your line in certain stretches. As soon as you hook them, they will put their heads in the gravel bottom and thrash their heads back and forth until they break you off. When you get down to 7x, it is a real chess match. You want to get their heads up to keep them from the bottom, but if it’s a bigger fish, you may break them off trying to get their head up. I would rather break them off trying to get their head up then let them get to the gravel bottom where it is virtually assured they will break you off.

Equipment Needs:

  • Rod: use one you can cast accurately in the 15-40 foot range.
  • Leader: I start with a minimum of a 9 foot tapered 5x leader. If I get refusals, I add on 2-3 feet of 6x tippet. If they are still refusing, drop to 7x.
  • As the season progresses I usually start with a 12 foot 5x leader. The fish get increasingly picky.
  • Flies – make sure you have 3-4 male and female patterns. I like to have 2-3 different types of wing material and body types. Sometimes the difference can be amazing. Remember, you will get broken off, that’s why you need 3-4 of each pattern.
    • Male patterns: 2-3 tail fibers, black body, black abdomen, spent wing material
    • Female patterns: 2-3 tail fibers, white or pale green body, black abdomen, spent wing material
    • If you tie your own, you can find patterns on the internet.
    • If you want to purchase them, your local fly shop and numerous internet sites can provide a nice variety of “styles”
    • Every year it seems like a different “style” works better than others do. Don’t be afraid to try different styles as well.
    • The drowned trico is very easy to tie. Add an appropriately sized glass bead and tie a female (white body, black abdomen). Tie the wings angled back at ~45 degrees. It is pretty easy to find a recipe on the internet.
  • Hook size – The flies are generally best imitated by #20-24 (or smaller) hook sizes. I always start with one hook size larger than the flies on the water. Use the biggest fly fish will take. You will land more fish. If the fish are not even looking at your fly it is either too large or your tippet is too heavy. I usually drop one hook size first (it’s faster to retie one fly). If the fish still don’t look at your fly, drop down one tippet size. Keep dropping your fly and tippet size until you get takes.
    • The size of the fly can be very important. These are small flies. If the naturals are 3 mms long and you are using a 4 mm imitation, the fish see a 30% larger fly. That is enough to keep them from taking the fly.
    • I started using Daiichi 1130 and 1140, or Tiemco 2487 hooks. They have a wide gape and 1x fine hook. This gives you more hook setting ability. In addition, I tie most of my trico patterns on a size #18 hook but tie #20 or 22 size bodies. The flies don’t float as well, so you have to use floatant more often, but I lose fewer fish.  
  • Floatant – use whatever you like, I find the dry powder (Frog’s Fanny and the like) works best, but rub on liquid floatants work well too.

Well, that’s it. This should get you going. Feel free to contact me if you have any questions. This is definitely a challenging way to catch trout. However, landing upper teens trout on a #18-20 hook with 5-6X tippet is a real achievement. So go get em! This is a true test of your fishing abilities.


  1. “So go get em! This is a true test of your fishing abilities”


    Very nicely done. I am sure there are many out there who will try and take your advice. I wish them the skill to be successful. We are blessed out here in Montana with massive Trico spinner falls in the summer months on many rivers. At times the river can just boil with fish and you wonder where they all came from. Many years ago I bought dozen Trico spinner imitations, probably size 18 or 20. For me, I’ve found them to be useless for two reasons—I can’t tie them to my tippets and I can’t see them on the water. Both of these conditions make for un-fun fishing. Not to worry though as trout feeding on Trico spinner falls, especially rainbows, can be a little impetuous. My barbaric solution is to chuck large Woolly Buggers along the edges of rising fish. The larger fish are usually along the edges of current seams where the Tricos float and hungry, impetuous trout generally won’t pass up entrees when surrounded with appetizers. Like you, I’ve learned when and where to be to on the rivers I fish to maximize results from the Trico fall. Some of the largest Browns and Rainbows I’ve taken have been such during events. Unfortunately my methods for doing so are to say the least: Barbaric.


    1. Hi Mike,
      You hit the nail on the head. If you fish only a trico pattern you would need telescopic vision to see your fly. That is why I stick with a two-fly rig. I use a #16 parachute (Adams, BWO, or Purple Haze) with a hi-vis post material (I may have forgotten to mention that in the article). That way I can always find the bigger fly (almost always) and know that the trico dropper is 15-18″ away. Usually I can find the trico.
      You also bring up another valid point. When the spinner fall is so thick it is difficult, nay impossible, to compete with the naturals. In those instances your “barbaric approach” makes complete sense.
      As always, one of the most important parts of becoming consistently successful on the river is to be flexible. If what you are doing isn’t working, you may as well try something different. You already know what’s not working so trying something “barbaric” may be the best solution. Besides, as long as the trout is big, I don’t care what I catch them on! Sounds like we share that attitude. Thanks for the great comments.

  2. I really, really, really like your bullet-list-style way of sharing your observations Joe; so well structured, so easy to peruse and retain the relevant points. You share predictive details (temperatures, the non-clock-hands focus, the seasons), and entomological lore, and practical aspects (rigs and methods that have worked for you) in a way that can be used and re-used as a reference. Excellent in every way.

    My guess is that the sheer biomass in such events is part of the reason trout love Trico spinners…and part of it is probably that they taste great! A trout’s “taste buds” surely evolved to make them “want” such a sustenance bonanza. Not that I’m going to test that theory between two slices of bread (even with Grey Poupon), but I think those trout frenzies point to the taste assumption as likely (also I guess their reasons don’t matter to us, as long as they plow those paths with mouths open across the run).

    I’ve not had a lot of experience with heavy spinner falls, and it’s clear I’d be ill equipped, fly-wise, if I stumbled into another one. The best I’ve done the few times I’ve witnessed anything remotely similar is the odd “consolation take” on some “wrong” pattern, in the vein of the one you described.

    But I think now I’ll be watching the calendar page and the thermometer, and scheming. I already tend to work with 6x and 7x tippets, so no big switch there. But I’ll go tie up a few of these (right after I find my double-magnifier reading glasses and purge my system of coffee for a few weeks…).

    Thanks for a really well delivered and much appreciated article; now I’ll go back and read it through again!

    – Mike

    1. Mike, well done on the info. I know guides that won’t even put their clients on the tricos, a testimony to the catch difficulty. I however cannot resist the swarms I see every morning from early July to September. The trick is to try to time your hook sets as the takes are quick and hard to see. Trying a visible lead fly helps and I find a chubby wing pattern on spinners invaluable for visibility. Once the hatch seems to be over go to the drowned spinner pattern. You will be presently surprised to find their still eating below.


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