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Mayfly Species Maccaffertium terminatum

Pictures Below
I have found no information about this species in angling literature, but one mediocre evening on the West Branch of the Delaware I found them to be a substantial part of the mixed bag of cahills and other mayflies causing a half-hearted rise of trout.  

Where & When


Regions: East, Midwest, West

Time Of Year (?): My collections were on June 7th in the Catskills

The Mayflies of the United States webpage shows this species distributed across the East and Midwest and West into the Rockies, although not quite to the Pacific slope.

Hatching Behavior


Time Of Day (?): Evening


Spinner Behavior


Time Of Day: Evening

I collected a male and female mating while flying downstream over the tail of a long flat, not in part of any concentrated swarm over a riffle. I saw many of the females flying over the water and dipping down to lay their eggs.

Pictures of 4 Mayfly Specimens in the Species Maccaffertium terminatum:

Specimen Page:12
Female Maccaffertium terminatum Mayfly SpinnerFemale Maccaffertium terminatum  Mayfly Spinner View 5 PicturesI was able to identify this female because I captured her while she was mating with an identifiable male.
Collected June 7, 2007 from the West Branch of the Delaware River in New York
Added to Troutnut.com by Troutnut on June 8, 2007
Male Maccaffertium terminatum Mayfly SpinnerMale Maccaffertium terminatum  Mayfly Spinner View 11 PicturesI positively identified this specimen under a microscope with a good key. It was one of the more common species in a generally light mixed bag of mayflies over a big Catskill tailwater last night.

I swooped this one out of the air while it was mating with a female, so I can be certain about her ID as well.
Collected June 7, 2007 from the West Branch of the Delaware River in New York
Added to Troutnut.com by Troutnut on June 8, 2007
Maccaffertium terminatum Mayfly NymphMaccaffertium terminatum  Mayfly Nymph View 1 PicturesThis is a subspecies (Subspecies: Entomologists sometimes further divide a species into distinct groups called subspecies, which have two lower-case words on the end of their scientific name instead of one. The latter is the sub-species name. For example, Maccaffertium mexicanum mexicanum and Maccaffertium mexicanum integrum are two different subspecies of Maccaffertium mexicanum.) M. terminatum terminatum, formerly called Stenonema. Found mostly in larger rivers in western Montana. This is an immature nymph.
Collected November 23, 2005 from the Flathead River-lower in Montana
Added to Troutnut.com by Bnewell on June 26, 2011
Specimen Page:12

Recent Discussions of Maccaffertium terminatum

Anybody know more about Maccaffertium terminatum? 3 Replies »
Posted by Troutnut on Jun 8, 2007
Last reply on Jun 11, 2007 by Konchu
I just wrote up what I found on the page for this species. I was mildly surprised to see so many of a species I've never seen mentioned in an angling context -- at least a few dozen throughout the evening. They piqued my curiosity.
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