The ‘bug of the month’ for March is the…March Brown. March Browns are mayflies that get their namesake for being, well, brown and for hatching in March. As with most common names for aquatic insects, the name March Brown can apply to several different species of mayfly. On the West Coast, the name March Brown applies to Rhithrogena morrisoni; while on the East Coast, it applies to Stenonema vicarium. This common name confusion is why insect taxonomists use the scientific names (even though those change often too!) to describe insects.
March Browns, like other members of the family Heptageniidae, are known as clinger mayflies in the nymph life stage. Their body shape is extremely flat and their gills often form a suction cup like structure on their underside. They are adept at living in the fastest riffles and can persist high flows without being dislodged like other species. Their persistence to stay where they are means they are not as available to salmonids as other species. Even though they are less available, they are often seen in the drift as they are extremely abundant. We do occasionally find the nymphs in the stomachs of juvenile salmonids; but it is much more common to see the adult life stage being eaten.
Adult March Browns are one of the most prolific hatches of insects in the winter months. Although they cannot meet the numbers of midges or Baetid mayflies, their larger size is a good source of calories for hungry salmonids. They typically hatch February through April although they are most abundant in, you guessed it, March. You will often see a hatch of March Browns bringing juvenile salmonids as well as larger trout to the surface. A March Brown imitation fished as a dry fly is a good way to catch an adult Steelhead in the spring.
Check out this March Brown fly tying tutorial from the Oregon Fly Fishing Shop:
Photo Captions
- A March Brown nymph. [Courtesy Rick Hafale]
- Here is a mature March Brown nymph showing it’s developed carapace/wing pad. [Adapted from Oregon Fly Fishing Blog Fly tying tutorial]
- A March Brown adult courtesy The Missoulian Angler Fly Shop. [Les Korcala]
Chris Laskodi, M.S., Fish Ecologist – Yurok Tribal Fisheries Department
Chris serves as the fish biologist/ecologist for the TRRP in the program’s Science branch. Chris has worked on the Trinity River since 2015, previously serving as a fish biologist for the Yurok Tribe and a fisheries technician for the US Fish & Wildlife Service. Chris holds a B.S. in Wildlife, Fish and Conservation Biology from the University of California, Davis and a M.S. in Aquaculture/Fisheries from the University of Arkansas at Pine Bluff. In his free time, Chris enjoys taking friends and family fishing on one of the many watercraft available to him.