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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
Baetis

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.

Lateral view of a Female Sweltsa borealis (Chloroperlidae) (Boreal Sallfly) Stonefly Adult from Harris Creek in Washington
I was not fishing, but happened to be at an unrelated social event on a hill above this tiny creek (which I never even saw) when this stonefly flew by me. I assume it came from there. Some key characteristics are tricky to follow, but process of elimination ultimately led me to Sweltsa borealis. It is reassuringly similar to this specimen posted by Bob Newell years ago. It is also so strikingly similar to this nymph from the same river system that I'm comfortable identifying that nymph from this adult. I was especially pleased with the closeup photo of four mites parasitizing this one.
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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Naaimzerox has attached this picture to aid in identification. The message is below.
Naaimzerox
Posts: 4
Naaimzerox on Dec 30, 2017December 30th, 2017, 7:55 am EST
Hello, what kind of mayfly is this? I mean the name with the species. Thank you for your help.
Taxon
Taxon's profile picture
Site Editor
Plano, TX

Posts: 1311
Taxon on Dec 30, 2017December 30th, 2017, 1:44 pm EST
Hi Naaimzerox-

I believe this female imago to be of family Heptageniidae. Where is from, and when was it photographed?
Best regards,
Roger Rohrbeck
www.FlyfishingEntomology.com
Naaimzerox
Posts: 4
Naaimzerox on Dec 31, 2017December 31st, 2017, 4:44 am EST
I found it at Ulu Yam, Selangor, Malaysia. it was 3 months ago. Thank you for your reply
Taxon
Taxon's profile picture
Site Editor
Plano, TX

Posts: 1311
Taxon on Dec 31, 2017December 31st, 2017, 8:30 am EST
Thanks. Am only able to find one mayfly species (of family Heptageniidae) listed for Malaysia, which is Atopopus malaysianus. However, absent either a description or photo for purpose of comparison to the very nice photo you submitted for identification, who knows :-)
Best regards,
Roger Rohrbeck
www.FlyfishingEntomology.com
Millcreek
Healdsburg, CA

Posts: 344
Millcreek on Dec 31, 2017December 31st, 2017, 8:42 am EST
I was able to find a couple of papers that list some mayflies for Malaysia and for Borneo. The links are below. The paper on Malaysian mayflies has a list starting on page 494.

http://www.tropecol.com/pdf/open/PDF_57_3/10%20Ghani%20et%20al.%20f.pdf

http://www.ephemeroptera-galactica.com/pubs/pub_s/pubsartorim2003p403.pdf

I looked further and found these photos under Thailand mayfly (google search) which look nearly identical to yours.

https://thailandwildlife.photoshelter.com/image/I0000UDik4riE7fg

https://thailandwildlife.photoshelter.com/image/I0000HnyisfBdMAU

Unfortunately, they do not list the mayfly by name, and as near as I can tell most Thai mayfly keys list nymphs rather than adults.
"If we knew what it was we were doing, it would not be called research, would it?"
-Albert Einstein
Naaimzerox
Posts: 4
Naaimzerox on Jan 1, 2018January 1st, 2018, 4:16 am EST
Thank you for all the information given. I will do more investigation. Any update is highly appreciated.
Naaimzerox
Posts: 4
Naaimzerox on Jan 1, 2018January 1st, 2018, 10:54 pm EST
In your opinion, can it be Electrogena lateralis?
Wbranch
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York & Starlight PA

Posts: 2635
Wbranch on Jan 2, 2018January 2nd, 2018, 2:38 am EST
Naainzerox,

I know nothing about entomology but was wondering why you would think your mayfly is Electrogena lateralis after reading this quote I found by Googling the name you provided;

Electrogena lateralis is a common, though localised species in Scotland, Wales and the North and South West of England. Nymphs of this species are typically found in riffle areas of rivers and streams, although they can also occasionally be found on the wave-lashed shores of standing waters.
Catskill fly fisher for fifty-five years.

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