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Spring is a funny time in the Rocky Mountains, weather alternating between the last of the winter blizzards and the warm, bright days of the coming summer. But for a fly fisherman, weather isn’t as important as you might suppose. In the big rivers something’s happening, a process of growth and change within the insect populations, and there’s a hatch that’s going to pop out soon regardless of the weather. It’s going to happen around Mother’s Day, May 8th.
This is no minor smattering of insects, no early season appetizer for the trout; it’s one of the "super hatches" on our western rivers and the fish gorge on the blizzard of bugs. The Mother’s Day insect is a caddisfly, more commonly known as the Grannom. The emergence occurs in late afternoon or early evening if the weather is sunny, and at midday if it’s overcast. This stage of the hatch is matched with a size 14 Emergent Sparkle Pupa pattern a flush floating dry fly with a dark brown and a bright green body.
The insects fly to the bank, mate, and then the females return to the stream to lay eggs. It’s during this stage that an adult imitation, such as the Elk Hair Caddis, becomes important. The problem is that both an emergence and an egg laying flight can occur at the same time, and fish will focus on either the pupa or the adult, not both. At such times you’ll have to experiment with two types of flies.
That’s the only tactical problem with the Mother’s Day hatch. When the trout are rolling and jumping, they’re easy enough to find. The largest trout hold at the heads of pools or flats, waiting in the slower water for the insects to drift down from the riffles.
The big rivers are usually in very good condition in May. The cool nights hold the snow up in the mountains, delaying the run off until June, and the waters run clear and low. An abnormally warm stretch of days or a heavy rainstorm can muddy a particular river, and while that may not stop the hatch, it does hurt the fishing. Call a fly fishing shop to check up to the moment conditions.
Here is a list of shops that can provide daily information on the best rivers in Montana for the May caddisfly hatches. They can also help you with the details of setting up a trip:
Beaverhead River – *Frontier Anglers in Dillon (*).
Yellowstone River – *Bailey’s in Livingston (*).
Big Horn River – *Classic Angler in Butte (*).
Lower Clark Fork River – *Streamside Anglers in Missoula (*).
Missouri River – *Montana Fly Goods in Helena (*).
The wonder of the Mother’s Day hatch is that even on popular rivers the visiting angler will have plenty of solitude. A river like the Big Horn, that will be mobbed with floaters and waders after the 4th of July, offers clear water, a heavy hatch, rising trout, and lonely runs and pools during the spring season. Come on out and enjoy the fun this spring! Gary La Fontaine.