**Mayfly Species Rhithrogena morrisoni (Western March Brown)**

Mayflies

Caddisflies

Stoneflies

Taxonomic Navigation -?-

Kingdom Animalia (Animals)

» Phylum Arthropoda (Arthropods)

» Class Insecta (Insects)

» Order Ephemeroptera (Mayflies)

» Family Heptageniidae (March Browns, Cahills, Quill Gordons)

» Genus Rhithrogena

» Species morrisoni (Western March Brown)

Common Names

Match	Common Name
	Western March Brown
	Western Black Quill
	Black Quill

These are the first sizable, fishable mayflies of the season on many Western trout streams.

Where & When

Region: West
Time Of Year (?): April to mid-June, but as early as February near the Pacific, and as late as September in places

There is wide disagreement in the angling literature about the emergence dates for this species. It may be that some authors have confused a different species into the mix, or this species may be especially subject to variation based on the wide range of thermal conditions throughout the West.

The daily hatch lasts from 1 to 2 hours.

Hatching Behavior

Time Of Day (?): Late morning on warm days; mid-afternoon on cool days

The duns leave their nymphal shucks (

View Full Size

Here's an underwater view of the pupal shucks of several already-emerged Brachycentrus numerosus caddisflies.

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.) on the bottom of the stream and float to the surface. They ride the surface for a long time to dry their wings, making dun imitations ideal.

Spinner Behavior

Time Of Day: Same as emergence

Spinner falls may sometimes be important.

Nymph Biology

Current Speed: All current speeds
Substrate: Gravel

This species is more tolerant of slow water than most in Rhithrogena, but it also does well in the very fast water typical of the genus.

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Jargon Defined:

Duns: Mayflies have two adult stages. They first emerge from the water as duns (scientifically known as the subimago stage). They then molt into the spinner (imago) stage, in which they mate and die. Sometimes the word "dun" is confusingly used to refer to a brownish gray color in fly tying materials.

Emergence: The transformation of a nymph or pupa into the adult winged stage of an insect. The term may refer to the emergence of an individual, or the daily or yearly event in which all individuals of a species emerge.

View Full Size

Here's an underwater view of the pupal shucks of several already-emerged Brachycentrus numerosus caddisflies.

Shucks: 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.

Spinner: There are two winged stages of adult mayflies. They emerge from the water as duns, molt on land (usually) into their fully mature stage, spinners. As spinners, they mate, lay eggs, and die.

Useful References:

Arbona, Fred Jr. 1989. Mayflies, the Angler, and the Trout. Nick Lyons Books.

Caucci, Al and Nastasi, Bob. 2004. Hatches II. The Lyons Press.

Knopp, Malcolm and Robert Cormier. 1997. Mayflies: An Angler's Study of Trout Water Ephemeroptera . The Lyons Press.

Swisher, Doug and Carl Richards. 2000. Selective Trout. The Lyons Press.