Updated: Jun 7
It might be the oldest trick in the trout fly fishers playbook. Swinging soft hackled flies has worked for hundreds of years and though not as popular today, it still tricks fish when nothing else does. Yet, many people still don’t really know why it works. Even in the videos scattered across the internet, anglers claim that we still don’t know why trout take swung soft hackles!
Surely there is a logical reason why swinging soft hackles elicit strikes. Better yet, if we understand WHY this strategy works, we will know WHEN to swing.
The most obvious reason a trout would eat a soft hackle is because they think it’s food. But surely the down and across swung presentation isn’t natural or common of their typical food sources…Though most trout food is taken as it drifts downstream into a fish’s mouth, other food sources are actually strong swimmers during certain life stages. On our home river, splashy aggressive rises are usually indicative of trout taking caddis in the upper water column. These rises really get your heart going, and demonstrate the burst of energy needed to capture caddis pupa and adults before they escape. Clearly, the trout know the speed of caddis and respond appropriately when feeding. This also shows that a split-second decision is made by the fish as they speed to capture their prey. But let's examine each insect guild as it relates to swinging soft hackles.
First, stoneflies. Stoneflies undergo incomplete metamorphosis (nymph -> adult) and emerge by crawling ashore and emerging on streamside vegetation. Not a likely candidate for swinging soft hackles.
Next, mayflies. Mayflies are a diverse bunch and can be subdivided into different lifestyle groups: swimmers, clingers, crawlers, and burrowers. All undergo incomplete metamorphosis. For anglers, these different types can be identified by their shape, and depending on the time, make much better candidates for swung soft hackle wet flies. Arlen Thomason suggests that mayfly duns (emerging mayflies) have hydrophobic qualities that allow emerging mayflies to avoid getting stuck in the surface film as they emerge. This quick rise through the water column could be an enticing approach to swinging soft hackles.
Swimmers are hydrodynamically shaped and move throughout the water column more easily than other mayflies. This group, which includes BWOs, Callibaetis, and Isonychias, make likely candidates for mimicry with swung flies.
Clingers are usually flatly shaped as they hold on to the surface of rocks, where they graze for algae and periphyton collecting on river rocks. These types of mayflies, including Brown Drakes and March Browns, aren’t as readily available to fish outside of when they are actively hatching.
Crawlers are more agile and active feeders than clingers, navigating the calm water in the interstitial space between rocks on river bottoms. Since they move more actively than clingers, they are more available as drifting food to trout. Western Green Drakes, PMDs, and Red Quills are crawlers but migrate to the bank before emerging but could make good candidates for swung wet flies If it’s the right time of year, and you’re on a river that supports these types of mayflies.
Burrowers are the least available as food, because (as their name suggests) they’re buried for most of their nymphal lives.
Now, caddisflies. Unlike mayflies and stoneflies, caddisflies undergo complete metamorphosis (larva -> pupa -> adult) in the water. Caddisfly larvae can either be free-living and predatory (active feeders), spin nets to collect drifting detritus (passive feeders), or case-building grazers (relatively inactive feeders). But when caddis pupate and pursue their adult life stage, they navigate swift currents to reach the surface. They may be strong swimmers but they are also vulnerable during this period and are often targeted by river-dwelling trout. Summer caddis can hatch for long stretches of time meaning caddis pupa are readily available, making them another excellent insect/hatch for swinging soft hackles.
Finally, midges. Midges also undergo complete metamorphosis in the water. As such, there is a period where midges emerge from their deep dwellings to rise to the surface for adulthood. Some may be surprised that sparkling flies like the miracle midge are actually imitative patterns for midge pupa. These emerging midge pupae fill with gas to help them elevate to the water’s surface, which gives pupae a sparkling appearance. Midges may be small, but offer another opportunity for swinging (appropriately sized) soft hackles.
Now, what about swing speed? A research team in Italy figured out that certain taxa (types of insects) tend to drift at different heights of the water column. They found that most types of insects drifted closest to the bottom, but certain types preferred drifting higher in the column. Swimmers were much more likely to drift in the upper water column, while unsurprisingly, benthic (bottom-dwelling) and crawler invertebrates tended to hangout lower in the water column. So you can tailor your swing speed to match which insects are present and hatching during your outing at appropriate water depths. An active caddis or mayfly hatch might mean faster swings higher up in the water column, while midge hatches or non-swimming mayflies may require a slower drift speed for your swing presentation.
What about Baitish? Though I think this would be best addressed in a streamer-focused article, baitfish also present opportunities for fishing soft hackled flies. Lots of classic (older) fly patterns could mimic small fry, and minnows. I’d prefer to fish larger soft hackles, like baitfish, during periods of turbidity or increases in stream flows throughout the entire water column (like during high run-off season).
But what is the fish actually sensing that merits the strike? If you’ve fished a down and across swung soft hackle, you know that the takes are very noticeable. Unlike a fish sipping dry flies, when a trout takes a soft hackle, you feel a stronger predatory response from the fish. It’s like the JV version of fishing streamers. When fish are feeding on nymphs they inevitably make mistakes, taste things, and reject certain objects. But you won’t have that issue with soft hackles, which are mostly presented to fish from their side. They have already made up their mind by the time you feel the jolt. Aside from the obvious visual cues, one theory suggests that vibrational sources in close proximity to a trout will elicit a strike. Therefore, the soft hackled feather on a fly might have properties picked up by a fish’s lateral line, but this means you need to get your fly right in line with an actively feeding fish, which can be difficult, especially if you’re not sight-fishing.
If the fish is picking up on visual cues, fear not. Trout have a large viewing window on either side of their body, though only viewed by one of their two eyes, meaning a fish could detect motion of a swung fly at some distance (depending on sun penetration and water clarity). I’ve read some general estimates that a trout’s viewing window is approximately 2.25 times the depth at which the fish is swimming. Coupled with the upward trend of the fly as you reach the end of your presentation, the fish might not have a lot of time to mad-dog your fly. By the time your soft hackle is visible, and with the assumption that the fish recognizes the fly as escaping prey, a split-second decision is made. This is much more forgiving than the long period of determination prior to a dry fly or nymph take in soft calm water. Not to mention that fish can view potential prey items with both eyes when presented directly in front of them. Finally, monocular vision isn’t as strong as binocular vision when perceiving depth perception, so the potentially unnatural swing across currents can possibly be negated by the lack of depth perception The fish has when viewing something with only one of its eyes.
So what flies should you use?
Since swinging soft hackles is all about motion, don’t sweat the details of fly patterns. The key component is the soft hackled feather used to push water and provide movement at the head of the fly. Some like sparsely hackled flies, others like heavily hackled feathers; both work, but it probably depends on the depth of the fish and the type of insects you’re aiming to mimic. But it’s easy enough to rectify depth changes with some split shot.
When’s the last time you swung a wet fly for trout? It might be time to try it again. It can be a very forgiving method to break up the standard paradigm of technical nymphing. Plus you could always dead drift soft hackled nymphs. But as runoff recedes, we could all use a break from flinging bobbers around, so take advantage. There will be plenty of time for that this winter.
Mayflies 101. The Perfect Fly Shop. http://www.perfectflystore.com/laquatici2.html
K. Christopherson. Sorting Out Mayflies. https://www.coloradofishing.net/ft_mayfly.htm
A. Thomason. 2009. Bug Water. Stackpole Books
S. Fenoglio et al. 2004. Vertical Distribution in the Water Column of Drifting Stream Macroinvertebrates. Freshwater Ecology 19:3.
T. Sholseth. 2003. How Fish Work. Frank Amato Publications.
How Do Trout See? Vail Valley Anglers. https://blog.vailvalleyanglers.com/how-do-trout-see/amp/
What Can Trout See? Trout Pro. https://www.troutprostore.com/class/what_can_trout_see