In the East and Midwest this is one of the most important hatches of the Spring. They are large flies which emerge sporadically, making for long days of good fishing.
» Species vicarium (March Brown)
This species contains the two classic Eastern hatches formerly known as Stenonema vicarium and Stenonema fuscum, the "March Brown" and "Gray Fox." Entomologists have discovered that these mayflies belong to the same species, but they still display differences in appearance which the trout notice easily. Anglers should be prepared to imitate both types. Where & When
Regions:This hatch begins in Pennsylvania and the Catskills in the middle of May. It peaks there in late May and early June. Throughout the rest of June and early July the hatch moves into the Adirondacks, New England, and the Upper Midwest.
East, MidwestTime Of Year (?):
Mid-May through early July
The best action lasts from 1-3 weeks in most places. The traditional March Brown duns originally in the vicarium species are more common toward the beginning of the hatch, while the former-fuscom Gray Fox variety take over in the latter weeks.Hatching Behavior
Time Of Day (?):The nymphs are reported to scurry from their fast-water habitat into slow pools and marginal water before emergence.
Late morning through evening, usually peaking mid-afternoon; only late evening on hot daysHabitat:
Slow waterWater Temperature:
March Browns take a long time (sometimes more than 30 seconds) to escape their shucks (Shuck: The shed exoskeleton left over when an insect molts into its next stage or instar. Most often it describes the last nymphal or pupal skin exited during emergence into a winged adult.) in the surface film, and then they ride the water for a long time and struggle through failed attempts to take flight. This hatch is exceptionally prone to producing cripples (Cripple: In fly fishing, a cripple is any insect which has been injured or deformed so that it cannot escape the water. This may include stillborn emergers or fully emerged adults which have been damaged, often by wind or waves, so that they can no longer fly. Trout often favor eating crippled insects.) and stillborns (Stillborn: In fly fishing, a stillborn insect is one which got stuck in its nymphal or pupal shuck during emergence and floats helplessly on the surface instead of flying away. It is a specific class of cripple, although it is sometimes used interchangeably with that term.).
These characteristics leave room for many types of flies: floating nymphs, emergers, low-riding duns, hackled duns, and cripple (Cripple: In fly fishing, a cripple is any insect which has been injured or deformed so that it cannot escape the water. This may include stillborn emergers or fully emerged adults which have been damaged, often by wind or waves, so that they can no longer fly. Trout often favor eating crippled insects.) patterns all have their place.Spinner Behavior
Time Of Day: Late evening through duskMarch Browns return to the stream as spinners a few days after emerging. Spinners from many days of hatching typically mate together on select nights, and this makes for inconsistent but exceptionally good spinner falls.
In Hatches II, Caucci and Nastasi write that the females oviposit by making repeated runs at the surface, dipping their abdomens briefly and rising up for another run. This contradicts the behaviors listed in Mayflies of Michigan Trout Streams, in which the Leonards say the females may drop their eggs from the air or release them as they fall spent (Spent: The wing position of many aquatic insects when they fall on the water after mating. The wings of both sides lay flat on the water. The word may be used to describe insects with their wings in that position, as well as the position itself.). Readers are invited to share their experiences in the comments and clarify the spinner behavior.Nymph Biology
Current Speed: All speeds, but best in fast waterIn Mayflies, the Angler, and the Trout, Fred Arbona reports stomach samples indicating the importance of these nymphs.
Substrate: Everything from boulders to weeds to leaf drift (Leaf drift: The mass of dead leaves gathered on the bottom of the stream, sometimes stacked thick in still places like back eddies. Many aquatic invertebrates use the leaf drift for shelter and food. Most insects shred the leaves to digest the bacteria and plankton living on them, rather than digesting the leaves themselves.) to silt
Environmental Tolerance: Very tolerant of high temperature and slow water
Trout appear to be aware of this phenomenon, for their stomachs will often be crammed with as many as 100 to 200 immature nymphs a week before the hatches will begin for the season.Maccaffertium vicarium Fly Fishing TipsThis hatch often occurs simulatenously with more concentrated species, and fish may be selective to those. Although March Browns provide good action throughout much of the day, you should not let them distract you from higher-density hatches of smaller flies like Ephemerella invaria which the fish might take selectively instead.
Pictures of 19 Mayfly Specimens in the Species Maccaffertium vicarium:
1 Streamside Picture of Maccaffertium vicarium Mayflies:
Recent Discussions of Maccaffertium vicarium
2 tails or 3 1 Reply »
Posted by Snagy
on Feb 5, 2010
Last reply on Feb 6, 2010 by Taxon
I notice that while the dun, nymph, and spinner photos on the page are all listed as March Brown (maccaffertium vicarium). While the coloration patterns all seem to follow other March Browns I have seen, I notice that the winged flies pictures all have 2 tails, but the nymphs in the photos have 3. I was under the impression this species was a 2 tailed mayfly. Is the nymph mislabelled?Replydiff between march brown &gray fox 7 Replies »
Posted by Jrcald
on Mar 12, 2007
i know that gray foxs and march browns are classified in the same family but what are the differences ? what is the color differences are both bodies the same color tan ? Reply
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