Trout eat more dead bugs than live ones

We all know a trout's diet is made up mostly of nymphs. Nobody is debating that.

But there's more to this story than what meets the eye.

What if I told you that given the choice, trout will selectively pick dead flies over live ones? And it happens both above and below the water.

The cripples nobody talks about

Plenty of studies have been done on trout diet and the one constant is that trout feed most of the time under the water, not on top.

That might lead you to believe they're eating live bugs the whole time. There's some truth to that. But it's not always true.

Vince Marinaro documented in In the Ring of the Rise that during a mayfly hatch, the trout at the seat of the rise were selectively taking stillborns and cripples over healthy duns. The ratio was often 3 to 1 or higher.

Marinaro wasn't the only one to notice it. Datus Proper spent a career arguing the same thing in What the Trout Said: trout systematically feed on the easiest, most vulnerable version of a bug available.

Gary LaFontaine watched it underwater with caddis in the 1970s. Ralph Cutter later put it on film.

None of them were scientists, they were anglers who spent decades looking closely. But when four careful observers, working with different bugs on different water across fifty years, all report the same pattern, that's the closest thing angling has to a settled fact.

The reason is simple. A cripple can't escape. It sits lower in the film, half in and half out, twitching and struggling but not going anywhere. A trout has learned that a cripple is a guaranteed meal. A healthy dun might lift off between the eat and the rise.

Spinner falls, the pure dead-bug event

Now here's where it gets really interesting. It's no secret that one of the biggest feeding windows in the whole season is a mayfly hatch, and every angler is glad to land on one.

But like the cripples above, once things move into the spinner phase the fish are on the dead ones.

After the mayflies mate, the females drop their eggs, and the females and males both fall to the water spent. Wings flat, bodies motionless, drifting.

You'll know it when you see rises to nothing.

That's the time to tie on a spinner. The bugs are lying flush in the film and you can't see them from the bank, but the fish can see them from below just fine.

The second act nobody stays for

Here's the part I really want you to take away. Most anglers pack up when the visible action ends. The hatch fades, the duns thin out, the rises get quiet, and the fly rods go in the tube.

But the drowned adults keep drifting. Dead mayflies, drowned caddis, egg-laying females that died on the water after their last flight. It all keeps going into the drift for another hour, sometimes more.

The big fish come out for this. It's the quiet second act of every hatch and almost nobody is around to fish it.

Terrestrials, the everyday version

Another food source often overlooked is terrestrials. Ants, beetles, hoppers, inchworms.

Most of these bugs fall in or get washed in and die. Trout feed on them for the same reason they feed on cripples: it's a guaranteed calorie with no chase.

Same story as the trout food you've been stepping on. Everything falling in from the land is a dead bug the moment it hits the water.

Why trout do this

Here's the method to the madness. Like most wild animals, trout have to balance effort against calories.

Think of the big trout that sit in the soft water behind a rock or under a cut bank. They let the food come to them. They don't chase. Chasing costs calories and it doesn't always end in a meal.

If a trout rises to a healthy fly and misses, that's spent energy. For a wild animal in cold water, that's a big deal. A spent mayfly, on the other hand, is a lot of calories for almost no effort. Every time.

There's real fisheries science behind this.

Kurt Fausch's drift-feeding model, published in 1984 and cited in salmonid research for the last forty years, shows that stream trout position themselves and pick targets to maximize net energy intake, the calories they take in minus the calories they burn to get them.

In the same year, Robert Bachman spent three seasons observing wild brown trout from camouflaged towers over a Pennsylvania stream and concluded that their feeding behavior was defined by net energy maximization achieved principally through cost minimization.

Which is the scientific way of saying they pick the easy meal every time. A crippled mayfly you can grab in the film is the definition of that. A dun that might fly is the opposite.

Given the choice, they take the sure thing.

What this means for your fly box

Here's what to actually do with all of it.

Fish cripple patterns during hatches. A Quigley Cripple, a sparkle dun, a Compara-dun tied a bit scruffy. Try one before you tie on a standard parachute.

My own go-to is the paraloop mayfly spinner, and it's no secret to anyone who fishes with me.

If you want something simple, a sparkle dun is often taken as a spent fly.

Carry spent patterns for the end of a hatch. A rusty spinner, a hen-wing spinner. Tie one on when the visible action stops and the rises go quiet.

Fish drowned versions when the water goes still. A wet caddis, a sunk mayfly. Ridiculously effective in the hour after everyone else has left the river.

And tie your dries a bit rough. Uneven hackle, dubbing hanging off, wings not quite right. It sits lower in the film. It looks like something that's struggling. Fish take it.

This is the whole reason ugly flies catch fish.

You can spend hours on a pretty mayfly pattern, and they truly are a work of art, but I guarantee you that my ugly spinner will outfish yours at least 3 to 1.

It's also the reason old flies outfish new ones.

A fly that's been in the jaws of a few trout, chewed up, waterlogged, and half falling apart, sits in the film like something that isn't going anywhere. Which is exactly the bug the fish is looking for.