This fly is tied on a size 10 hook and originally imitated a Stonefly Lava. As the name indicates it hails from the state of Montana, USA where it is used on the Yellowstone and Missouri rivers. In the UK it has proved a good fly on lakes and reservoirs: every bit of the fly, from the black chenille body to the Firefly Lumi thorax, screams fish catcher. Cast to likely looking spots using either a floating or sinking line, the retrieve can be very slow or extremely fast, all these options work depending on the day. The pattern is suitable for use on lakes and can be used all season.