Michigan Flies

Hatches / mayfly

Isonychia

A

Isonychia bicolor (also I. sadleri)

Also called Iso, Slate Drake, Mahogany Dun (Iso), Leadwing Coachman, White-Gloved Howdy.

The fourth of the Au Sable's Big Five, with a June peak and a second September peak that gives some of the best fall dry-fly fishing. Nymphs are strong swimmers in fast cobble water and crawl out on rocks to emerge, leaving shucks on the stones, so a swum or stripped #10-12 Iso nymph is the primary fish-catcher, and the spinner fall in late evening over moderate current is the surface event. Fall duns often emerge midday and trout do take them on the water; a #12 Adams or Borcher's Drake covers the dun and spinner. Starts the first week of June on the Muskegon and runs sporadically to September.

#8–14eveningduskmiddaynymphdunspinnerdark mahogany to reddish-brown bodyslate gray wingdark brown nymph with pale dorsal stripemale spinner intensely red with white fore-legs

© Steven Joyner · CC BY · iNaturalist · Jasper Township, MI · 2024

Timing by region

  1. Southeast Lower Peninsula
    1. J
    2. F
    3. M
    4. A
    5. M
    6. J
    7. J
    8. A
    9. S
    10. O
    11. N
    12. D
    Window
    May 1 – Sep 16
    Peak
    May 18 – Jun 16
  2. Southwest Lower Peninsula
    1. J
    2. F
    3. M
    4. A
    5. M
    6. J
    7. J
    8. A
    9. S
    10. O
    11. N
    12. D
    Window
    May 5 – Sep 20
    Peak
    May 22 – Jun 20
  3. Northeast Lower Peninsula
    1. J
    2. F
    3. M
    4. A
    5. M
    6. J
    7. J
    8. A
    9. S
    10. O
    11. N
    12. D
    Window
    May 15 – Sep 30
    Peak
    Jun 1 – Jun 30
  4. Northwest Lower Peninsula
    1. J
    2. F
    3. M
    4. A
    5. M
    6. J
    7. J
    8. A
    9. S
    10. O
    11. N
    12. D
    Window
    May 15 – Sep 30
    Peak
    Jun 1 – Jun 30
  5. Upper Peninsula
    1. J
    2. F
    3. M
    4. A
    5. M
    6. J
    7. J
    8. A
    9. S
    10. O
    11. N
    12. D
    Window
    Jun 5 – Oct 21
    Peak
    Jun 22 – Jul 21

Flies that match

Borchers Parachute (reference photo)Reference photo
Borchers Parachute
A
Dry fly#10–16Dark turkey-quill body, brown hackle

Grayling's dark all-purpose mayfly, listed by Hawkins in #10 to #16 for Mahogany and Isonychia spinners. It doubles as a Hendrickson and Black Quill dun in spring and a fall Mahogany Dun on the Pere Marquette from mid September through October. Fish it at dusk for Iso spinner falls from June through September.

Dry fly

Reserve · $3.00
Adams (and Parachute Adams) (reference photo)Reference photo
Adams (and Parachute Adams)
A
Dry fly#10–20Gray (standard)Slim-bodied #10-12 for Gray Drake

Michigan's own fly, born on the Boardman, and still the default searching dry on every river in the state. Hawkins recommends a slim-tied #10 to #12 Adams for Gray Drake spinner falls at dusk on the Pere Marquette and Muskegon, and smaller sizes pass for most gray-winged mayflies from April through October.

Dry fly

Reserve · $3.00
Gold-Ribbed Hare's Ear (reference photo)Reference photo
Gold-Ribbed Hare's Ear
A
Nymph#8–18NaturalOliveBeadhead

The generalist buggy nymph for Michigan's clinger mayflies and caddis pupae, and MidCurrent lists a #10 to #14 Hare's Ear among winter steelhead nymphs. Dead-drift it under an indicator all season for trout, and as a trailer behind an egg or stonefly for steelhead.

Indicator nymphing · Euro / tight-line nymphing

Reserve · $2.75
Isonychia Parachute (reference photo)Reference photo
Isonychia Parachute
A
Dry fly#8–12Mahogany body, slate wing

Isonychia is one of the Au Sable's Big Five, hatching in two peaks, June and September, from mid May to the end of September. The nymphs crawl out to emerge, so Michigan guides fish nymphs and spinners more than duns; use this parachute as a spinner or searching dry on evening riffles, and midday in fall.

Dry fly

Reserve · $3.00
Isonychia Nymph (reference photo)Reference photo
Isonychia Nymph
A
Nymph#8–12Dark brown with pale dorsal stripe

The fished stage of the Isonychia on Michigan rivers, since the strong-swimming nymphs migrate to the bank to crawl out. Swing or twitch it through cobble riffles in the evening from June to September on the Au Sable, Upper Manistee, Boardman and Muskegon.

Indicator nymphing · Euro / tight-line nymphing

Reserve · $2.75