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Lateral view of a Male Baetis (Baetidae) (Blue-Winged Olive) Mayfly Dun from Mystery Creek #43 in New York
Blue-winged Olives

Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.

27" brown trout, my largest ever. It was the sub-dominant fish in its pool. After this, I hooked the bigger one, but I couldn't land it.
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Mayfly Family Polymitarcyidae (White Flies)

This is the only family of burrowing mayflies, besides Ephemeridae, which is abundant in the United States. All the trout fly fishing action comes from the genus Ephoron, because the other two genera reside in warm waters in the South.

Read about Ephoron for more details.

Where & when

In 81 records from GBIF, adults of this family have mostly been collected during August (36%), July (31%), September (16%), June (10%), and October (6%).

In 38 records from GBIF, this family has been collected at elevations ranging from 618 to 6250 ft, with an average (median) of 3691 ft.

Family Range


To determine whether a specimen of Ephemeroptera belongs to Polymitarcyidae, use the Key to Families of Mayfly Nymphs or Key to Families of Mayfly Duns and Spinners.

1 Streamside Picture of Polymitarcyidae Mayflies:

Discussions of Polymitarcyidae

Posted by Imaxfli on Oct 23, 2020 in the species Ephoron leukon
Last reply on Oct 23, 2020 by Imaxfli
Me too looking for photos or better yet, video of matching. These things seem to pop outa the water like no other ......
Polymitarcyidae Question
1 replies
Posted by Steamntrout on Jun 22, 2017 in the species Ephoron album
Last reply on Jun 22, 2017 by Crepuscular
What size are these nymphs & Sub Imago's?
Fly choice during an Ephoron hatch
13 replies
Posted by Jmd123 on Aug 3, 2007 in the genus Ephoron
Last reply on Jan 31, 2016 by Martinlf
Hey folks, what would you recommend as an imitation of these guys? They're hatching furiously in the Huron River in/near Ann Arbor, MI (smallmouth are leaping out of the water to eat them). How about a Light Cahill or White Wulff? Both have been major producers for me on other streams with white mayfly hatches in summer (e.g., Rifle River). If anyone has a particular recipe that works for them, I'd like to know. Thanks!

Potomac White Fly Hatch - in progress
1 replies
Posted by BrettB on Sep 17, 2008 in the genus Ephoron
Last reply on Sep 21, 2008 by GONZO
There's quite a big white fly hatch on the Potomac at least around Harper's Ferry. Does anyone know a good nymph or emerger pattern for the white fly hatch? I plan to hit it early, prior to duns coming off and know there is a good deal of nymphal movement and drift beforehand. Maybe I'll collect a few tonight to see color / size / behavior. Any thoughts are appreciated.
Ephoron Leukon nymph photographs
11 replies
Posted by BFornadley on Feb 8, 2007 in the species Ephoron leukon
Last reply on Aug 14, 2007 by Gene
I need some help here. I have been looking all over the web for someone who may have taken some Ephoron Leukon nymph underwater (or out of water) photos.I saw the description here at "Troutnut.com" and advice that a smaller Brown Drake (Ephemera) nymph would be a good natural to use as a tying model but I really want to see the real thing. Does any body have any of these pics or can anyone definitively tell me where to look?

Start a Discussion of Polymitarcyidae

Mayfly Family Polymitarcyidae (White Flies)

Genus in Polymitarcyidae
EphoronWhite Drakes
Genus in Polymitarcyidae: Campsurus, Ephoron
2 genera (Tortopsis and Tortopus) aren't included.
Family Range
Common Name
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