The Improved Montana Stone is a traditional all-purpose nymph. What’s unusual about it is its very simple construction. It’s made of one feather and a six-inch piece of wool yarn (not counting the chassis – hook, lead and thread.)
I’m a big fan of yarn as a material for sub-surface flies. It’s quicker, easier and probably cheaper than dubbing fur onto tying thread, and creates a natural, slightly rough-looking body with built-in segmentation. You can separate the yarn into plies to make smaller flies or use it as is for the larger models.
Speaking of larger models, I brought a handful of IMS to the Farmington River in Connecticut, which thanks to Mother Nature, the Hartford water supply district and the Connecticut Department of Energy and Environmental Protection is chock full of sizable trout.
It’s unusual to catch anything smaller than an honest 12 inches on the Farmington, and if you do catch anything smaller than that it’s a wild trout, which is always nice. People who know the river well land 20-inchers on a regular basis. I’m not one of them, but having grown up on skinny 9-inch hatchery yearlings over the state line in New York, I enjoy the Farmy’s plump, 12-inch browns.
The IMS was met with approval by a few handsome trout and one acrobatic show-off bass during a couple of brief sessions over the weekend.
As its name suggests, the Improved Montana is a stonefly pattern, but I figured it would be a good Isoynchia nymph in size 10 and the fish didn’t disagree.
The wing case did pop loose on one fly after a tussle with a trout. So the IMS isn’t exactly bomb-proof. But it’s so easy to make, I consider it expendable.
You’ll find the recipe and how the fly came to be on page 74 of Simple Flies: 52 Easy to Tie Patterns That Catch Fish.