Ants fall onto the water all summer, and trout eat them with confidence because a real ant can't crawl out once it's stuck in the film. The Fur Ant copies that profile: a fat back hump and a fat front hump of dubbed fur, pinched to a thin waist, with a turn or two of hackle around the middle for legs and just enough float to keep it riding flush.
Tie or buy it in sizes 14-20. Black is the default and covers most carpenter and field ants; cinnamon matches the smaller red ants common near streamside grass and timber. Go smaller on flat, clear water and pressured fish.
This is a low, clear-water fly. Fish it on a dead drift, the same as any small dry, but expect it to sit in the surface film rather than perch high on top, so it can be hard to see - track its drift line and watch for the actual sip instead of setting on shadows. It works best on warm, calm summer afternoons with water in the mid-50s to mid-70s, when no hatch is on but fish are looking up. It is a good searching pattern and a strong second fly below a hopper. After a windy day, fish it tight to the bank where ants blow in.