Cinnamon ants are the most underrated summer dry fly on Colorado tailwaters. From late June through September, Formica and its relatives — the reddish-brown ants that blanket streamside vegetation — get blown or knocked into flat water and seams, and selective trout eat them with confidence. Size #16–18 cinnamon ant patterns, fished flush in the film or on a parachute, will pull fish at Deckers and Cheesman Canyon that won’t look at anything else mid-morning.
Why Cinnamon Ants Trigger Selective Feeding on Tailwaters
Aquatic hatches on tailwaters are predictable enough that the fish pattern them. Midges at first light, BWOs on overcast afternoons — the trout know the schedule. Terrestrials break that script. A cinnamon ant doesn’t emerge on a cycle; it falls off a willow branch or gets blown off a grass stem, lands hard, and sits flush in the surface film. There’s no warning, no pre-hatch nymphing phase to cue the fish up. It’s a single trigger — the fly hits flat water and a trout that’s been ignoring your midge presentation tips up and eats.
That opportunistic quality is what makes ant fishing exciting and what makes it tricky. The fish aren’t in a rhythm. They’re cruising slicks, sitting under shaded banks, holding in foam lines — and they key on the silhouette and flush profile of the natural. When ants are on the water and the fish know it, they get selective about it fast. I’ve watched fish at Deckers refuse a foam-body ant two sizes too large, then eat a #18 dubbed cinnamon on the next drift without hesitation.
The other thing working in your favor: cinnamon ants are abundant. Colorado streamside habitat is loaded with Formica species all summer, and any afternoon breeze shakes them loose. You don’t need a “hatch” in the traditional sense. Wind is your trigger — a steady mid-morning or early afternoon breeze along a willow-lined bank means ants are falling, and it’s time to switch. It’s about the only time a Colorado breeze is doing you a favor instead of parking your fly in the nearest willow.
Cinnamon Ant Pattern Selection: Foam vs. Dubbed Body, Flush vs. Parachute
Not all ant patterns fish the same water, and the difference between a foam-body and a dubbed-body ant matters more than most people think.
Dubbed Body Fur Ants (Flush-Floating)
The Fur Ant Cinnamon is the pattern I reach for first on flat, slow water — the glassy slicks below riffles, the long pools at Cheesman, and anywhere fish are feeding with selective, deliberate rises. A dubbed ant sits lower in the film than a foam version, which is closer to how a natural ant actually rides. The segments — two distinct dubbing balls with a pinch waist, a sparse thread thorax, and a few hackle fibers or a hackle wrap — create an accurate silhouette from below.
Sizes: #16 and #18 are the workhorses. Size 16 works early in the season or when a mix of larger ants are on the water; go to 18 on pressured fish in clear, low flows.
The problem with flush-floating ants is visibility. A #18 dubbed cinnamon on flat water at 30 feet is nearly impossible to track. Solutions: use a sighter tippet, watch the fish instead of the fly, or pair it with a more visible dry as your lead fly in a dry-dropper setup (more on that below).
Foam Body Ants
Foam ants — a pinched or stacked foam body, often with a hot-spot head or rubber legs — float higher, last longer, and are dramatically easier to see. Colorado Fly Supply carries a Flying Cinnamon Ant and a Black Ant that cover the ant window well. Foam shines in two situations: broken water where a dubbed body would waterlog and sink within a few drifts, and as your indicator dry in a dry-dropper rig where you need it to hold a nymph without disappearing.
Sizes: #16–18 in foam. The thicker body reads as larger even at the same hook size, so I tend to fish foam ants one size larger than the dubbed equivalent.
Parachute Ants
A Parachute Ant — cinnamon dubbed body, white or pink parachute post, one or two hackle wraps — solves the visibility problem without sacrificing the low-riding profile. The parachute post doesn’t lift the fly unnaturally; the body still lands flush. It’s my go-to for late-morning sessions on the Cheesman flats when I’m fishing solo and need to track the fly across a long, glassy drift. Colorado Fly Supply’s Parachute Ant Hi-Viz is the version I’d point you at — one fly, two jobs.
| Pattern Style | Best Water | Size Range | Visibility | Notes |
|---|---|---|---|---|
| Dubbed Fur Ant Cinnamon | Slicks, flat pools, glass tailouts | #16–18 | Low | Most accurate film profile; hardest to track |
| Foam Ant Cinnamon | Broken water, dry-dropper rigs | #16–18 | High | Best flotation; reads slightly larger |
| Parachute Ant Cinnamon | Flat water, solo fishing, long drifts | #16–18 | Medium-High | Low body profile with visible post |
| Flying Ant / CDC Wing | Late summer flying ant falls | #18–20 | Medium | Match winged naturals when swarmers are present |
How to Rig a Cinnamon Ant on a Long Leader with 6X
This is where a lot of anglers leave fish in the river. The rig matters as much as the pattern.
Straight dry fly setup: A 9-foot tapered leader extended to 12 feet total with a 6X fluorocarbon tippet. On Cheesman and Deckers flat water, start at 5X and drop to 6X the moment they refuse — these fish are educated enough to read a heavy tippet on a small ant in clear, low summer flows. If you’re going to 7X, do it consciously: you’ll land fewer fish in fast currents but you’ll get more strikes in technical situations.
Tie the ant directly to the tippet. No loops, no snaps — just a standard clinch or improved clinch. Keep the knot as small as possible so it doesn’t affect the fly’s sit in the film.
Dry-dropper setup: This is how I fish ants most of the time — the same dry-dropper logic as everything else on this river. Lead fly is a foam ant or parachute ant in #16, which gives me enough flotation to hang a small dropper — typically a size 20–22 midge pupa or a small Pheasant Tail — 12 to 16 inches below on 6X or 7X. The ant serves as both an imitation and an indicator. When a fish takes the dry, I set. When the dry hesitates, twitches, or dips, I set — that’s the dropper getting eaten. This rig covers both the surface and the film simultaneously, which matters on tailwaters where fish might be keying on one or the other on any given day.
Leader taper for ant fishing: I run a standard 9-foot 4X or 5X tapered leader, add 18 inches of 5X, then 24–30 inches of 6X to the fly. Total leader is 12–13 feet. On calm flat water, the longer the better — less line on the water means less drag. Reach mends and pile casts before the line even lands are more effective than mending after; every on-water mend risks twitching a flush-floating ant and blowing the presentation. On flat water the fish are grading your drift, and they don’t grade on a curve.
My take
Dubbed cinnamon ants in #16 and #18 are the pattern I don’t leave home without from July on. Foam ants are more convenient and I respect what they do in a dry-dropper setup, but the take on a flush-floating dubbed ant in flat water is something else — the fish comes up slow and deliberate, not the slashing take you get on a hopper. Parachutes solve the visibility problem without giving up too much. The real mistake people make isn’t the pattern, it’s going too big — a #12 or #14 foam ant in low, clear water at Cheesman gets refused more than it gets eaten.
Where Do Trout Eat Cinnamon Ants on the South Platte?
Almost always within a rod’s length of the bank — foam lines, the slicks below riffles, and shaded grass- or willow-lined edges where ants actually enter the water. Ants don’t fall from the sky in the middle of the river, so the good ant water is rarely the pretty mid-river seam.
Location is the whole game with terrestrials. They enter the water from the bank, from overhanging willows, from streamside grass — which means productive ant water is almost always close to structure. If you want the longer view on reading that water, the same current-and-cover logic applies; ants just narrow your focus to the edges.
Foam Lines and Current Seams
Foam lines are your first target. Foam collects on the slow side of current edges, and it collects everything the river is carrying — food, debris, and cinnamon ants. A fish holding behind a mid-river rock or in a soft seam at the edge of a riffle has a delivery service running past its nose. Put the ant in the foam line and let it drift. Don’t move it; let it run the seam end-to-end before picking up.
Slicks Below Riffles
The tailout of a riffle dumping into a pool or run creates a slick — smooth, glassy water that collects everything washing off the riffle. This water looks quiet but it holds fish actively feeding on whatever the riffle is delivering. An ant drifting through a riffle tailout is an easy meal for a fish parked in a flat behind it. Cast above the slick, mend immediately, and let the ant swing through naturally. This is where the parachute ant earns its keep — visibility in those glassy tailouts is critical.
Shaded Banks in Late Morning
By 9–10 a.m. on a July day in Cheesman Canyon or along the cottonwood-lined banks at Deckers, trout push toward shaded banks. Shade does two things: it holds fish in comfortable water temperatures and it positions them directly under the vegetation that’s dropping ants. Work within 12 inches of the bank — seriously, that tight. Cast parallel to the bank, keep your leader off the grass, and drift the fly along the grass line. The willows will eat more of my ants than the trout do, and they never give one back. The takes in this water tend to be quiet and subtle — a slow tip-up from a fish that’s already positioned exactly where it wants to be.
Wind-exposed banks deserve special attention. The downwind bank is where blown ants accumulate. On afternoons with any kind of sustained breeze, I’ll move to the bank that’s taking the wind and work it hard. Forget the pretty mid-river seam — fish the shore.
When Does Cinnamon Ant Fishing Peak on the South Platte?
Late June through September, with July the heart of it and warm, windy afternoons the daily trigger. Terrestrial season on Colorado tailwaters runs all summer, and ants are on the water any time a breeze is knocking them off streamside vegetation.
July is the strongest month. Ant populations are at peak density, fish are looking up and feeding opportunistically, and afternoon breezes are consistent enough to keep ants falling. Cheesman Canyon and Deckers are both productive start to finish. It’s one leg of the broader terrestrial season — the ants, beetles, and hoppers that take over the banks once the grass is high.
August extends the window, but heat can push fish into cooler, deeper water in the middle of the day. I shift to early morning and late afternoon then, with midday fishing near inlet flows or shaded canyon sections. Same fish, same fly — you just work around the thermometer instead of pretending it isn’t there.
Late morning through afternoon is the prime window — roughly 9 a.m. on, as the breeze builds. Ants are active on streamside vegetation, the wind picks up, and fish hold in feeding lanes rather than retreating to depth. On overcast days it runs all day.
Flying ant falls — the winged swarmers that emerge in late summer — can trigger some of the most intense ant feeding of the season. When you see winged ants on the water, match them with a CDC Flying Ant or Flying Ant Cinnamon in #18–20. These events are unpredictable but when they happen, every fish in the run is looking up.
Presentation: Dead Drift, No Drama
Ants don’t swim. A natural ant on the surface sits flush in the film, moves with the current, and doesn’t twitch. Your presentation should match that exactly.
Dead drift is non-negotiable. Any drag — even micro-drag that’s invisible from your position — will get the fly refused by fish that are keying on ants. The upstream presentation works well in riffle tailouts; on flat pools and glides, the downstream approach (positioning above the fish, casting down, feeding slack) puts the fly over the fish before the leader and is harder to drag. Practice the reach cast and the pile cast — both are more useful on ant water than any mend you can make after the line lands.
Don’t set too fast. Ant takes on flat water are deliberate. The fish tips up, opens its mouth, takes the fly down — and if you set on the first flash of white mouth you’ll pull it out before it closes. Let the fish turn, then set. The old British dry-fly governor works perfectly here: when the trout takes, say “God Save the Queen,” then lift. For a big fish sipping in slow glass, add the King. It feels absurd right up until it saves you the three fish an itchy trigger finger would have pulled off the hook.
If you’re fishing the dry-dropper and you can’t tell if the eat was on the dry or the nymph, set anyway. On calm water you can usually see which fly disappeared.
Frequently Asked Questions
Q: What size cinnamon ant fly should I use on the South Platte in July? #16 and #18 are the most effective sizes for Cheesman Canyon and Deckers. In low, clear summer flows, #18 is the right call for pressured fish. Size 16 is the pick early in the season, when a mix of larger ants are on the water, or in faster, broken water where fish have less time to inspect.
Q: Should I use a foam ant or a dubbed fur ant for tailwater fishing? Dubbed fur ants in cinnamon sit lower in the film and produce more strikes from selective fish in flat water. Foam ants float longer, are easier to see, and are the better choice as the lead fly in a dry-dropper rig. Use both — they do different jobs.
Q: What tippet should I use for cinnamon ant patterns? 5X to start and 6X the moment they refuse, for #16–18. Drop to 7X in the most technical situations on calm, clear water. Run a 12-foot total leader for flat tailwater pools — the extra length keeps more fly line off the water and reduces drag.
Q: When is cinnamon ant fishing best on Colorado tailwaters? Late June through September, with July the peak and late morning through afternoon the most consistent daily window. Windy days and afternoons with a steady breeze blow ants off streamside vegetation and onto the water, concentrating fish along foam lines, shaded banks, and riffle tailouts.
Late summer on the canyon water is one of the best stretches of the year precisely because most anglers walk past ant-eating fish to go chase whatever hatch is supposedly on. The fish feeding on cinnamon ants in the slicks and along the grass-lined banks aren’t the most visible risers — they’re subtle, opportunistic, and often the biggest fish holding in that stretch. A #18 dubbed fur ant on a 12-foot leader with 6X, drifted tight to a shaded bank or through a foam line — that’s a hard setup to beat from July through the end of summer. Keep the box stocked and pay attention to the wind.
Next: ants are one leg of the terrestrial season — the South Platte hatch calendar shows where they sit against the hoppers and beetles.