Photo by Steven Mlodinow

Callibaetis Overview

  • Family: Mayfly
  • Size: 10-16 mm (Size 12-16)
  • Emergence: May through August
  • Emergence Time: Late morning through early afternoon

The Callibaetis hatch in Montana is a strong hatch for our stillwater fisheries, notably Georgetown Lake. The Callibaetis hatch is often a blanket hatch, and lake fish have an interesting way of dealing with this hatch. Trout will attack this hatch by “gulping.” This is defined as trout moving in a straight line, rising rhythmically through the blanket hatch. When fish are gulping, you need to lead the fish and drop the fly in the next place the fish will rise. Few other hatches create trout behavior like this

Fly Fishing The Callibaetis Hatch

The most prominent feature of the Callibaetis is their exceptionally thin body. Make sure the imitations you have are sparse and thin for better imitation. Hafele and Hughes, in their book Western Mayfly Hatches, state the trout focus on the spent female adults. Those insects offer the easiest targets, and fish key on them. Additionally, as the season progresses, the Callibaetis will get smaller and smaller. They start as a 12 in the beginning of the hatch, which is late spring, but may be size 16 by the end of the summer. The Callibaetis hatch in the mid-morning, and will hatch until the afternoon winds come and screw things up! Many anglers will leave when the wind starts, but the crafty angler will utilize the waves to give a Callibaetis nymph its proper action (up and down) and continue to take fish above the weed beds.

Callibaetis Nymph

The Callibaetis nymphs live in the weeds on the bottom off the lake. Float over a weed bed, and you need to hope you don’t swallow an adult, they can be so prolific. The nymphs display an interesting behavior. They will exit the weeds, swim up and then swim back to the weeds. They will do this until they decide to come to the surface to hatch. You’ll see trout hammering these nymphs as they expose themselves above the weed beds.

This is a premier hatch on Montana’s stillwater’s. If you’re lake fishing in July and August, make sure you have a wide selection of Callibaetis fly patterns.

Additional Callibaetis Resources