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Mayfly Species Stenacron interpunctatum (Light Cahill)

Pictures Below
This is the best of the sporadic summer hatches known to anglers as Light Cahills. It was formerly known as Stenonema canadense and is considered by most angling historians as the model for that classic Catskill pattern.  

Where & When


Regions: East, Midwest

Time Of Year (?): Mid-May through late August, peaking in late June and early July

Stenacron interpunctatum emergence is quite sparse, but it can be important because there is so little competition on the water on late-season evenings.

The best hatching in the East is in late June an early July, and in the Midwest this species peaks about a month later.

Hatching Behavior


Time Of Day (?): Sporadically all afternoon and evening in cool streams; concentrated in the evening in warm weather

Habitat: Slow water

This species emerges more gracefully than the related duns of Maccaffertium and Stenonema, and emerger patterns take on less importance. They drift for a while as duns, and that is the stage to imitate, although the nymphs preparing for emergence can also be of value.

Spinner Behavior


Time Of Day: Twilight or after dark; may be earlier on cloudy days

Habitat: Riffles
Stenacron interpunctatum flies return to the stream as spinners a couple days after hatching.

The females oviposit while laying on the water.

Nymph Biology


Current Speed: Medium to fast

Substrate: Gravel, detritus (Detritus: Small, loose pieces of decaying organic matter underwater.)

Environmental Tolerance: Tolerant of warm temperatures, but not pollution

Pictures of 3 Mayfly Specimens in the Species Stenacron interpunctatum:

Female Stenacron interpunctatum (Light Cahill) Mayfly DunFemale Stenacron interpunctatum (Light Cahill) Mayfly Dun View 6 PicturesThis is a fairly small late-season female Stenacron dun.
Collected August 22, 2006 from the West Branch of Owego Creek in New York
Added to Troutnut.com by Troutnut on August 23, 2006

1 Streamside Picture of Stenacron interpunctatum Mayflies:


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