Stenonema Vicarium  March Brown nymphs are one of the most important food sources of the early season for trout in our area.  Imitations of 12 and even 10 work well in the higher flows of spring runoff.  The nymphs are clingers and can be found in faster water attached to rocks and logs.  They are not strong swimmers and should be fished with a dead drift.  They hatch in mid-May and usually come off the water sporadically making the dry imitations good ones to prospect the water with instead of casting to steady risers.  They take a long time to hatch so emerger and floating nymph patterns can be effective.