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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.

Dorsal view of a Amphizoa (Amphizoidae) Beetle Larva from Sears Creek in Washington
This is the first of it's family I've seen, collected from a tiny, fishless stream in the Cascades. The three species of this genus all live in the Northwest and are predators that primarily eat stonefly nymphs Merritt R.W., Cummins, K.W., and Berg, M.B. (2019).
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 Species Isonychia serrata (Slate Drakes)

Where & when

In 1 records from GBIF, adults of this species have been collected during June (100%).

In 1 record from GBIF, this species has been collected at elevation of 1721 ft.

Species Range

Physical description

Most physical descriptions on Troutnut are direct or slightly edited quotes from the original scientific sources describing or updating the species, although there may be errors in copying them to this website. Such descriptions aren't always definitive, because species often turn out to be more variable than the original describers observed. In some cases, only a single specimen was described! However, they are useful starting points.

Male Spinner

Body length: 14 mm
Wing length: 13 mm

A species having purplish brown markings on a bronze abdomen, and dark venation.

Head brown. A black mark below the frontal margin. Reddish purple spot on each side of median carina; another on outer side of base of antenna. Pronotum brown. Mesonotum yellowish brown margined with cream color; a yellowish spot anterior to the scutellum, which is dark brown. Metanotum and sternum dark brown. Pleura pale with brown and purplish markings. Fore leg purplish; femur grey at base and apex; tarsus light greyish purple. Distal half of last joint of fore tarsus and base of claws purple. Middle and hind legs white, last tarsal joint and claws purplish grey. Venation dark purple brown.

Abdomen bronze dorsally, the posterior half of each tergite purplish brown; wide dark posterior margins. A paler mid-dorsal line is present, bordered by oblique dark submedian streaks. Pleural fold and postero-lateral angles very dark brown. Ventrally dark purplish brown, except for the pale antero-lateral angles, a very narrow pale posterior margin bordered by the dark central color, an oblique pale submedian dash and four pale dots arranged transversely across each sternite near the center. On sternites 6-9, the lateral margins are also pale. Narrow dark bar parallels the pleural fold posteriorly on each sternite; at its anterior end is a dark dot. Tails very dark brown, slightly paler distally. In basal portion, joinings slightly paler brown. Forceps and forceps base yellowish or bronzy brown. Forceps base very slightly excavated on its apical margin; penes of the Isonychia arida type, the incurved lower portion bearing 7-8 saw-like teeth (see fig. 125).

Female Spinner

Body length: 14 mm
Wing length: 13 mm

In female, purplish markings at the corners of the occiput and between the eye and the lateral ocellus. Subanal plate of female almost straight across the apical margin, its outer angles rounded.

Start a Discussion of Isonychia serrata


Mayfly Species Isonychia serrata (Slate Drakes)

Species Range
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