In many parts of the Western U.S. the hint of a false Spring is teasing us out of our Winter doldrums. The first significant hatch of a large Mayfly is the March Brown (this is where I am suppose to throw in that fancy entomological Latin name, but I will forego the science side for now). Suffice to say that with moderating temps rising into the higher 40’s and 50’s coupled with overcast days the March Browns will be hatching in late February and well into April, even May in some areas.
Knowing the habitat of this ‘clinger’ nymph is important in your presentation. The nymphs hang in heavier water or riffles in that small layer of calm near the bottom. Once the momentum is made to emerge the nymphs can let loose and drift in the currents to slightly calmer waters or crawl to those calmer waters. From that point on the process of the hatch can be somewhere between the bottom and en route to the surface or at the surface film.
Beefy ‘clinger’ nymphs in a darkish tone, size 12 can work proceeding what is often an afternoon hatch. Swinging Wet flies up through the water column can work and of course the Emergers and Dry fly patterns are worthy once surface action is noted.
If your trout waters are open in February to April then you will enjoy the fishing of the larger March Brown (12-14) (compared to Winter’s Midges and BWO’s). The weather will often be unsettled, but worth the elements.
“Rhithrogena morrisoni” Western March Browns (for you smarty pants) and info on the Eastern March Brown as well.