A simple, classic, well balanced, and very natural-looking fly pattern. The insect March Brown is a mayfly, and most March Brown patterns imitate that in some sense ? as a nymph or emerger.
From the US when they have large hatches of mayflies in March, just after their winter, hence the name March Brown.
Fish this when the mayflies are around on a floating line with a long leader using a very slow figure of eight retrieve.