Photo by Steven Mlodinow

Hexagenia Overview

  • Family: Mayfly
  • Size: 30mm (Size 8 extended body)
  • Emergence: Early July through August
  • Emergence Time: Dusk to about 1:00 AM

Missoula anglers can boast of having the largest mayfly in Montana. Found in the Seeley Lake/Swan Lake area, the Hexagenia hatch in Montana starts appearing late June, and will hatch sporadically until the end of July. Measuring a whopping 30mm long, Hexagenias are burrowing nymphs, and need a muddy bottom to thrive.

From the fly fishing anglers standpoint, it’s a bit of an annoying hatch. On hot days, they don’t even start hatching until dusk, and will emerge for 2 hours, taking you into complete darkness. Not an easy hatch to see, you kind of need to hope for a bit of moonlight to see where the fish are coming up. Compounding the difficulty, the spinners fall as the adults are emerging, adding a level of complexity to the Hex hatch.

Fly Fishing The Hexagenia Hatch

The nymphs are strong swimmers, so when you go subsurface, a stripping motion is often productive. The nymphs are active swimmers, so your imitation needs to be active, not inanimate. Once the nymph gets to the surface, they emerge into adults very rapidly. However, the adult may sit on the water for quite some time as their wings dry and harden enough to fly.

Sometimes, as the Hexagenia is attempting to fly away, that movement will attract a trout to the natural. Be ready to apply a little movement to your bug. But make sure it’s an effective ploy. It’s been our experience on some nights that any movement of your line and leader will drive the fish away. You’ll need to explore the correct presentation for the night.

A boat or float tube is very useful for fishing the Hex hatch. It’s rare that Hex’s hatch near the shore,they are more a mid-lake phenomenon. You’ll need to get to the fish. Additionally, they don’t always hatch in the same place for long, so some nights you find yourself chasing rises.

Why chase this hatch? Because the biggest fish in the lake will come to eat the Hexagenia. Big food means big fish! Take a net!

Additional Hexagenia Resources