Why Bright Flies Are Effective

Bright flies can act as “attractors,” stimulating a fish’s curiosity or triggering an aggressive, territorial, or predatory response.

Hopper fly bin, Sula, MT.

For years, I’ve fished a small freestone creek in the Colorado foothills that’s populated with fairly sophisticated brown trout. The fish aren’t particularly big, but they live close to human development and activity, so they’ve adapted their feeding patterns to coincide with kids, dogs and increasing numbers of anglers. Evenings, low light conditions, even rainy days, are generally more productive than bluebird afternoons.

But yesterday, I decided to switch things up. The plan was to fish the creek in the middle of the day on a holiday weekend with some of the brightest flies (Bunyan Bugs) in my box. I wasn’t expecting a whole lot, but you never know–it’s fishing, and rule breaking should be a fundamental aspect of any angler’s development. As legendary fly-fishing guide Kea Hause once noted, “I never wake up in the morning with an agenda, no set plan. I have hunches and ideas, but I don’t make final decisions until it’s time to cast.”

At the creek, the conditions weren’t particularly inspiring: unremarkable bug activity, half feral dogs, screaming kids, men drinking expensive, artisanal beverages, throwing rocks in the river–at one point, I may have muttered to myself, this is easily the dumbest fishing decision I’ve made this year…

I rigged up and waited, then waited a little more. Eventually, it clouded up and threatened to pour, the barbecue parties and dogs cleared out and the fish slid out to their feeding lanes. You can probably figure out how the rest of the story went–any decently placed cast with a large, bright stonefly had fish swinging over for a look. Some ate, some didn’t, but the size, color and movement of the bug were eliciting trout interest and activity. For twenty minutes, I sized down to a smaller, darker fly, and the fish wouldn’t touch it. Back to the big, bright one and BLAMMO!

For the fly angler, particularly beginners and intermediates, getting to see fish interest and activity (and observing their behavior in the process) is one of the key ways to accelerate your learning curve. How fish are interacting with your flies is often the most critical information to gather on a fishing trip and one of the most overlooked. It can provide a ton of feedback about where fish live, their “activity” levels and how they gather prey. You’re trying to unlock a complex and continually evolving puzzle and every new piece of information brings the picture into clearer focus.

Fishing with bright flies can often be a great way to trigger and provoke fish reactions, while also eliciting, at times, milder “interested” responses. Any way you slice it, fish interacting with your flies is a good thing and provides valuable insights into their location and behavior. Most happy and active fish can be caught, if you haven’t spooked them initially with your approach. But you have to see them first, or trick them into exposing themselves. Gaudier patterns can be an effective way of getting fish to “play.”

So, how do flashier, brighter flies work?

Asking Google Gemini for an answer provides this generic response, “Brightly colored flies can be remarkably effective in fly fishing due to a combination of factors, primarily centering on visibility, attraction and the ability to provoke a strike from fish. While subtle, natural imitations have their place, vibrant hues often play a crucial role in an angler’s success…”

It’s not a terrible answer for an AI chatbot, but here’s a more thorough breakdown of the hows and whys of fish “bright fly” behavior.

Increased visibility: This is the most obvious and significant reason. If fish can see your flies, there’s a chance they might eat them. If they can’t see your flies, your chances are generally doomed, unless they can “feel” your flies, which often happens in dirty water with larger, bulkier patterns that push water (streamers).

Dirty or murky water: In water with reduced clarity from sediment, runoff or rainstorms, brightly colored flies allow fish to locate the patterns more easily. They may not always eat the pattern, but you can often see the fish and their reaction. Wading anglers might get another shot with a different colored pattern…

Low light conditions: During dawn, dusk, or overcast days, bright flies can be more visible to fish as ambient light diminishes. It may also be easier for anglers to track the patterns, particularly dry flies with bright wings or parachute posts.

Deeper water: As light penetrates deeper into the water column, certain colors, especially those with fluorescent qualities, can remain more visible than darker, drabber patterns. This is probably one of the main reasons brightly beaded nymphs are so effective: they provide flashes of color in deeper, darker water.

Attraction and curiosity: Bright flies can act as “attractors,” stimulating a fish’s curiosity or triggering an aggressive, territorial, or predatory response, even if the fly doesn’t precisely match a natural food source. Sometimes a flash of bright color can elicit an impulsive strike from a fish that might not be actively feeding but reacts to a sudden, conspicuous object. This is particularly true for predatory species, or fish in spawning and/or migratory modes.

Signaling prey: While not always a direct imitation, bright or flashy colors can mimic certain elements of natural prey, such as the iridescence of a baitfish’s scales, the bright spots on some insects or crustaceans, or even clusters of fish eggs. Flies with colored “hotspots” or strands of Krystal Flash and Flashabou can fall into this group–variations of darker, more realistic patterns with subtle, but highly effective, splashes of color.

Contrast: Against various underwater backgrounds, whether it’s dark, cobbled riverbeds, spring creek weeds, or open blue water, bright colors can provide contrast, making flies “pop” and easier for fish to detect. It’s also worth noting that the natural coloration patterns of fish and prey already provide elements of contrast in the wild: the sculpin or eel’s white underbelly, a trout’s brightly tipped fins, the dark, haloed spots on a redfish tail. These contrasting colorations are often referred to as countershading, a common evolutionary adaptation that serves as a crucial form of camouflage. Seen by predators from below, the sculpin’s white belly can blend with the lighter sky and water; from above, their darker mottled backs blend with the substrate. The iconic Dolly Llama (black and white) streamer provides a great example of contrasting visual elements that can be incorporated into an “impressionistic” fly pattern.

UV (ultraviolet) fluorescence and reflectance: Many bright fly-tying materials incorporate UV fluorescent or reflective properties, i.e. Antron yarns, Zylon, Sparkle Yarns, synthetic dubbings, Flashabou, Krystal Flash etc. Certain species of fish (many salmonids) can see a broader spectrum of light than humans, including UV, and these enhanced visual properties can make bright flies particularly enticing underwater, even when they might not appear overly bright to the human eye above the surface. A lot is made of fish having “small brains,” which may be true, but their eyesight is highly evolved and advanced. I spent many years fishing “mud season” on the lower Colorado River, and fish vision can become remarkably adaptable when the conditions warrant.

Be a “color sober,” but inquisitive angler.

While bright flies are undeniably effective, they aren’t a universal solution to most complex angling scenarios. In clear water, when fish are selectively feeding on specific insects, or when dealing with spooky, pressured fish, more natural, subdued presentations are often preferable.

I wouldn’t plan on showing up to Idaho’s Henry’s Fork or Silver Creek this fall during a Mahogany mayfly hatch, so you can start slinging pink and flesh colored Dolly Llamas. Even the greatest fishing “hunches and ideas” have limits…

The effectiveness of bright flies will largely depend on water conditions (clarity), light levels, your target species and even the mood of the fish on a particular day. Be smart and carry a wide selection of flies in various colors and brightness levels to adapt to changing circumstances.

You also should integrate your color theories in varying levels of subtlety–intentionally drab flies with purposeful “hotspots” are much different presentations than chartreuse takeovers of classic standards.

Plan to experiment, iterate and evolve. And if what you’re doing isn’t working, wipe the slate clean and try something new. The beauty of fly fishing is that it doesn’t hand out participation trophies–your approach is either working or failing, and failing often teaches us more, because these difficult lessons tend to hang around longer and, hopefully, motivate change.

The Irish writer and nihilist, Samuel Beckett, once famously penned in his 1983 novella, Worstward Ho, “Ever tried. Ever failed. No matter. Try again. Fail again. Fail better.” He was likely talking about the struggle of being a novelist and playwright, but he might as well have been talking about the pursuit of fly fishing. The writer’s blank page or the riverman’s miles of unexplored river–both uniquely challenging environments that reward curiosity, creativity and hard work. And if you threw your life away in the pursuit of either, it wouldn’t be the worst thing in the world…

---

“I had a dream as a kid”: Mark Engler has been a Colorado fly-fishing guide for decades, searching for northern pike and Rio Grande trout on dry flies. You know he throws bright flies.