Fly Fishing Isonychia Bicolor Mayfly Pattern

On the rivers of southern Ontario where I usually fish, Isonychia bicolor mayfly used to hatch normally right after Green Drakes, which is around the beginning of June, and than, a sporadic hatch during the summer and again in the middle of August. This was in the past. Today this is all different, unfortunately.

This article would only concentrate on describing Isonychia bicolor mayfly and how to fish trout following this hatch.

Isonychia dun is large size mayfly (but not as large as Green Drake) with grayish-brown bodies and dark -slate colored wings when taking flight. Front legs are dark but middle and hind are yellow, which gives the name bi-color. Along the water’s edge, numerous rocks held empty Isonychia nymph shucks lined in neat rows. This type of emergence tells me that using my nymph imitation is the most important stage of fishing and suggests that dry-fly fishing is not to be very manageable. Exception is high water level and windy days when dry fly fishing makes my day. When Isonychia times come, to emerge, the nymph migrates to the shallows and than it crawls up and out of the water on the rocks along the shoreline.

Hatching activities usually occur during the afternoon and early evening hours. On cloudy, overcast days this activity may continue sporadically throughout the day.

Nymph Presentation

Approach the stream cautiously and observe the water you are going to fish to develop fishing strategy. Cast the weighted nymph pattern upstream at an angle to get the nymph down deep quickly and drag-free. Use tuck cast to get a fly quickly to the bottom of the river. Isonychia nymph is a good swimmer and slight twitching of the rod tip helps to suggest the swimming action of natural insect. This is not necessary if you fish unweighted imitation close to the bank, which is also very productive technique since natural migrate to the short line just prior to emerging. Tip: Trout hit Isonychia nymph hard, so raise the rod tip quickly to set the hook.

Fly Fishing Isonychia Bicolor Mayfly Pattern
Isonychia Bicolor Mayfly Nymph Pattern – tied by Dimitri Ristic

Dry Fly Presentation

As it was mentioned earlier, fishing dry fly normally only happens on overcast days when casting across and down for the proper drift produce top dry fly fishing.

Fly Fishing Isonychia Bicolor Mayfly Pattern
Isonychia Bicolor Mayfly Dun Pattern – tied by Dimitri Ristic

Spinners Presentation

After the dun rest on nearby vegetation for a day or so, the insect changes into dark maroon spinner. Isonychia spinner’s body color is normally reddish-brown with clear wings.

Most duns emerge and spinners fall from 6PM to 8PM. However, late in the fall, spinners might be falling in the morning as well. I like to use the time before they fall to the water to get my proper position for casting. Spinner action lasts only 30 to 60 minutes, but can really make your day. Large trout usually migrate to shallow waters going after those spinners. The best spinner falls occur when the air temperature is 60 to 70 degrees Fahrenheit. This ideal air temperature could vary during the day, so does spinner action, all depending on air temperature.

Isonychia Bicolor Mayfly Spinner Pattern – tied by Dimitri Ristic

Presentation is always critical. You can select the perfect fly in the perfect size, but it means very little if the fly is not delivered on target and absolutely drag-free, especially on the smooth clear pools, flats and gentle riffles. A reach cast with slack line downstream is most defective one to use to eliminate the drag and micro drag (the one you can not see but trout can). Also, present the fly to the trout, not the leader or line.

Understanding and imitating natural insect’s appearance and behavior is the most important factor in your fly- fishing success.

Dimitri

About Dimitri Ristic

An avid fly fisherman and fly tyer for over 50 years. A master fly tyer with extensive knowledge of entomology. Dimitri's specialty are realistic flies. When he is not by his vise, you can find him on one of the river banks of Southern Ontario.

2 Comments

  1. JORGE LUIS SAUGAR on May 14, 2020 at 10:17 am

    Hola amigos, soy Jorge desde Argentina, por estos lugares en que vivo, tenemos varios lagos y ríos parecidos a los que ustedes pescan, la descripción que hacen de esta hermosa mosca, es perfecta en cada uno de los estadíos. La divulgación en FROSTYFLY, es muy valorable. Desde ya muchas gracias. JORGE-PATAGONIA ARGENTINA

    • Boris on May 16, 2020 at 2:42 pm

      Jorge, thank you very much for your feedback! We are glad that you found it useful. Tight lines!

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