Isonychia

NYMPH SIZE: 13-19 mm (1/2 to 3/4 in)

NYMPH COLOR: Black, dark red-brown

DUN SIZE: 13-19 mm (1/2 to 3/4 in)

DUN COLOR: Wing: dark gray with mottling. Body: gray, red-brown

SPINNER SIZE: 13-19 mm (1/2 to 3/4 in)

SPINNER COLOR: Wing: clear. Body: dark red-brown or gray

OTHER CHARACTERISTICS: Nymphs: slender shape; long hairs on front legs; three fringed tails. Duns and spinners: two tails; large hind wings

Mouse-over for alternate views: Nymph    Nymph 2    Dun    Spinner

About Isonychias

Isonychia mayflies are strong swimmers, and live in moderate to fast flows. They are not important everywhere; in fact, they are of no importance whatsoever on most rivers. But where they occur, they are often found in good numbers and can generate aggressive and selective feeding from trout. They hatch during the summer months.

Prior to emergence, the nymphs migrate to slower water. During the migration, many drifting in the flow and are taken by trout. This creates the most productive fly fishing opportunity: dead-drifting nymph imitations near the bottom.

Nymphs crawl out of the water and onto to dry land to emerge, so there is little point in fishing a dun imitation. However, spinner falls can be important.

STAGE

PATTERN

SIZE/
COLOR

PRESENTATION

WHERE

Nymph

A. P. Black

8-10/Black

Indicator, Tight line

Slow-moderate runs

A. P. Nymph, Hares Ear

8-10/Dark red-brown

Indicator, Tight line

Slow-moderate runs

Spinner

Hen Spinner

8-10/Dark red-brown

Standard dry fly

Slow-moderate runs