Ever see those national reports about clouds of insects so dense they show up on radar and coat entire towns? Those living blizzards are Hexagenia limbata, the giant mayfly that hatches at dusk in late spring and early summer throughout the Midwest. What makes these bugs so special is that they draw huge brown trout—the ones that spend most of their time hunkered deep—to the surface for a sip. But cashing in on this hatch is no sunny wade in the park. Here's how to stalk the dark of night and score in the swarm.

Rig Up

This game is about casting large flies in tight spaces and fighting big fish in close quarters. Medium-action 5-weight outfits are standard, but 6- and even 7-weight sticks aren’t overkill. Any well-dressed floating line will do, and all you need between line and fly is 6 feet of 10-pound-test mono or 2X leader material. “Fine and far off” is not operative here.

Down Note

Solid hooksets are easier to achieve with fish rising downstream of your position.

Cast Close

When you hear a rise, ease into a position that lets you make a short, accurate cast. You can get absurdly close to a Hex-feeding trout because it’s dark, the bottom is soft, and they’re so keyed in to the bugs. Don’t worry if your fly drags a little, either; sometimes that’s exactly what it takes to make it stand out from the parade of naturals floating by. Strike with conviction whenever you sense a splash in the vicinity of your fly. Side pressure helps keep fish out of snags.

Stake in the Mud

The Hex is a lover of silt, marl, and mucky sand. Look for duns to emerge in the slower sections of streams where a soft bottom predominates. Ideal water temperature is between 65 and 70 degrees, and the hatch typically begins 30 to 40 minutes after sunset. Deep river bends, undercut banks, and woody snags are classic spots; stake them out well ahead of nightfall, and don’t forget the DEET.

Nightly Specials

Battle gear for blackout browns.

1. Nealy’s Hex & Hex Polyback Emerger

Nealy’s Hex & Hex Polyback Emerger
F&SCliff Gardiner & John Keller

The rubber-legged Nealy's is irresistible to browns feeding hard on duns, whereas the low-profile Polyback is tops when the hatch slows and the fish become more selective. $2.75; tightlinesflyshop.com

2. Petzl Tikka Headlamp

Petzl Tikka Headlamp
F&SPetzl

A reliable headlamp is a must for catching a nighttime Hex hatch. This unit is so light and compact, you won’t even know you’re wearing it, and the high-output LED guarantees you’ll find your way back to the truck. $30; petzl.com.

3. Scott Radian Fly Rod

Scott Radian Fly Rod
F&SScott

Without visual cues to guide your casting, feel becomes all-­important—and in my opinion no rod has better feel than the Radian. The 8-foot 6-inch 5-weight is a terrific tool for this big-bug event. $795; scottflyrod.com