Great Western Leadwings

Mayflies

Caddisflies

Stoneflies

Scientific Name

Match	Scientific Name
	Isonychia

This common name refers to only one genus.

Mayfly Genus Isonychia

These are very rarely called Great Western Leadwings.

Sporadic hatches are rarely as outstanding as those of Isonychia. On streams with good populations, they are reliably hatching in light numbers, here and there, for most of the evening through most of the mid- to late season.

The spinners, and occasionally the duns, produce more concentrated action, but the real value of the Isonychia hatch is its duration and the size of the flies; large trout become ever watchful for them, even when they aren't emerging.

All the species of Isonychia are similar in appearance and behavior.

Isonychia bicolor (Mahogany Dun) Mayfly Nymph

View 7 PicturesThis Isonychia bicolor nymph from the Catskills displays the prominent white stripe sometimes characteristic of its species. This is the first such specimen I've photographed, because members of the same species in the Upper Midwest have a more subdued stripe (and were once thought to be a different species, Isonychia sadleri). The striking coloration on this eastern nymph is more appealing.

Collected April 19, 2006 from in
Added to Troutnut.com by on April 21, 2006

Female Isonychia bicolor (Mahogany Dun) Mayfly Dun

View 13 Pictures

Collected June 14, 2005 from in
Added to Troutnut.com by on May 26, 2006

Male Isonychia bicolor (Mahogany Dun) Mayfly Spinner

View 15 PicturesI got several really nice pictures of this spinner. I also collected a female on the same trip.

Collected August 9, 2006 from in
Added to Troutnut.com by on August 11, 2006

See 17 more specimens...

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.

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.