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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.

Dorsal view of a Setvena wahkeena (Perlodidae) (Wahkeena Springfly) Stonefly Nymph from Mystery Creek #199 in Washington
As far as I can tell, this species has only previously been reported from one site in Oregon along the Columbia gorge. However, the key characteristics are fairly unmistakable in all except for one minor detail:
— 4 small yellow spots on frons visible in photos
— Narrow occipital spinule row curves forward (but doesn’t quite meet on stem of ecdysial suture, as it's supposed to in this species)
— Short spinules on anterior margin of front legs
— Short rposterior row of blunt spinules on abdominal tergae, rather than elongated spinules dorsally
I caught several of these mature nymphs in the fishless, tiny headwaters of a creek high in the Wenatchee Mountains.
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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Male Callibaetis ferrugineus (Speckled Dun) Mayfly Spinner Pictures

This is one of four specimens I photographed together from the same hatch, also including a nymph, a male dun, and a female dun. According to the key in Check (1982), the clear wing venation on the associated dun shows that it is either Callibaetis ferrugineous or Callibaetis pallidus, and the characteristics to tell the difference between those two are maddening for both the nymph and adult. If the partial shading in the wing is "medium to dark brown," and the dots on the body are "fuscous to dark brown," then it's ferrugineous. If the wing shading is "chestnut brown" and dots on the body are "yellowish to chestnut brown," then it's pallidus. However, several spare specimens I collected alongside the one in the photo have no markings on the wing at all, which would seemingly indicate ferrugineous according to the key. It's enough for a contingent ID, but I still wouldn't rule out pallidus.

Lateral view of a Male Callibaetis ferrugineus (Baetidae) (Speckled Dun) Mayfly Spinner from Mystery Creek #304 in Idaho
Ventral view of a Male Callibaetis ferrugineus (Baetidae) (Speckled Dun) Mayfly Spinner from Mystery Creek #304 in Idaho
Male Callibaetis ferrugineus (Baetidae) (Speckled Dun) Mayfly Spinner from Mystery Creek #304 in Idaho
Dorsal view of a Male Callibaetis ferrugineus (Baetidae) (Speckled Dun) Mayfly Spinner from Mystery Creek #304 in Idaho
Ruler view of a Male Callibaetis ferrugineus (Baetidae) (Speckled Dun) Mayfly Spinner from Mystery Creek #304 in Idaho The smallest ruler marks are 1 mm.
Male Callibaetis ferrugineus (Baetidae) (Speckled Dun) Mayfly Spinner from Mystery Creek #304 in Idaho

This mayfly was collected from Mystery Creek #304 in Idaho on July 23rd, 2022 and added to Troutnut.com by Troutnut on January 15th, 2023.


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Male Callibaetis ferrugineus (Speckled Dun) Mayfly Spinner Pictures

Collection details
Location: Mystery Creek #304, Idaho
Date: July 23rd, 2022
Added to site: January 15th, 2023
Author: Troutnut
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