**Male Ephemerella aurivillii Mayfly Dun Pictures**

Mayflies

Caddisflies

Stoneflies

Classification

Kingdom Animalia (Animals)

» Phylum Arthropoda (Arthropods)

» Class Insecta (Insects)

» Order Ephemeroptera (Mayflies)

» Family Ephemerellidae (Hendricksons, Sulphurs, PMDs, BWOs)

» Genus Ephemerella (Hendricksons, Sulphurs, PMDs)

» Species aurivillii

This dun was collected in proximity to this spinner, and to this female that looks like the same species.

Among western species, it most closely resembles Ephemerella aurivillii, of which I reared a specimen from a positively-identified nymph and photographed the male dun previously in Alaska. In the photos, this dun does not seem to have the same evidence of the nymph's dorsal (Dorsal: Top.) stripe, but that's due to the lighting. A faint stripe is apparent under the microscope, as it is in the female linked above.

They do appear to be a bit short for aurivillii, with the male at 8 mm and the female at 9 mm, but the spinners could be a bit longer.

Among the other Ephemerella mayflies documented in Montana, Ephemerella alleni and Ephemerella mucronata are the only two others that seem to not be ruled out.

This mayfly was collected from the Madison River on July 1st, 2019 and added to Troutnut.com on July 18th, 2019.

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Male Ephemerella aurivillii Mayfly Dun from the Madison River in Montana

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Jargon Defined:

Dorsal: Top.

Dun: 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.

Nymph: The juvenile, underwater stages of mayflies, stoneflies, dragonflies, and damselflies and other aquatic insects whose juvenile stages are covered by hard exoskeletons. The word can also refer to the fishing flies which imitate these creatures, in which case it is used as a blanket term for flies imitating any underwater stage of an invertebrate (except for crayfish and leeches).

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.