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Lateral view of a Female Hexagenia limbata (Ephemeridae) (Hex) Mayfly Dun from the Namekagon River in Wisconsin
Hex Mayflies
Hexagenia limbata

The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.

Dorsal view of a Holocentropus (Polycentropodidae) Caddisfly Larva from the Yakima River in Washington
This one seems to tentatively key to Holocentropus, although I can't make out the anal spines in Couplet 7 of the Key to Genera of Polycentropodidae Larvae nor the dark bands in Couplet 4 of the Key to Genera of Polycentropodidae Larvae, making me wonder if I went wrong somewhere in keying it out. I don't see where that could have happened, though. It might also be that it's a very immature larva and doesn't possess all the identifying characteristics in the key yet. If Holocentropus is correct, then Holocentropus flavus and Holocentropus interruptus are the two likely possibilities based on range, but I was not able to find a description of their larvae.
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 Plauditus dubius (Tiny Blue-Winged Olives)

This species may produce good hatches.

Where & when

Time of year : July and August

In 12 records from GBIF, adults of this species have been collected during June (42%), July (25%), August (17%), September (8%), and May (8%).

In 4 records from GBIF, this species has been collected at elevations of 50, 1181, 1220, and 6250 ft.

Species Range

Nymph biology

Substrate: Gravel, vegetation

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 Nymph

Described in Ide (1937) as Pseudocloeon dubium
Body length: 3.2–4.1 mm

This species shows considerable sexual dimorphism in the nymphal stage, the males having contrasting pale and dark maculation and the females being more obscurely marked.

Head and mouth parts: Pale.

Thorax: Pronotum pale in medial area, laterally scattered brown markings on pale background; mesonotum mostly brown with small irregular paler areas; wing pads pale; legs pale, slight darkening at end of tibia and tarsus; claws pectinate.

Abdomen: Very strikingly marked, segments 3 and 4 and 8-10 being pale with the exception of submedial dark dots in the middle of the segments, segments 1 and 2 with more extensive dark areas and segments 5-7 dark with pale anterolateral corners and flanges; venter of segments 5-7 with median and lateral dark patches; caudal filaments pale with a conspicuous dark band half way out, the median filament relatively long, being about as long as the width of a lateral filament at the base; gills on segments 1-7 without distinct tracheae. The Ottawa river males differed somewhat in minor points. They were slightly larger (4.1 mm.); thorax more uniformly brown and on abdominal segments 8 and 9 four instead of two submedian dots; gills with faint tracheae.

Female Nymph

Described in Ide (1937) as Pseudocloeon dubium
Body length: 4.2 mm

This species shows considerable sexual dimorphism in the nymphal stage, the males having contrasting pale and dark maculation and the females being more obscurely marked.

Head: Vertex with submedial series of brown marks forming an irregularly convoluted line.

Thorax: Brownish with scattered obscure paler areas.

Abdomen: Not as strikingly marked as in the male; mostly dark with small pale areas along the anterior borders of the segments forming a median row and similar pale areas at the posterior borders of the segments forming a submedian row; lateral pale areas on the flanges and a submedian row of dark dots on the dorsum; venter uniformly pale except for dark tracheae laterally; caudal filaments as in the male; gills with fairly distinct tracheae.

Male Spinner

Described in Needham et al (1935) as Pseudocloeon chlorops
Body length: 2.5-4 mm
Wing length: 3.5-4.5 mm

Abdominal tergites of male imago hyaline whitish with a faint yellowish tinge.

Turbinate eyes the size of those in P. dubium (now a synonym of Plauditus dubius); in living insect, yellowish green with a purplish-brown band at the base of the stalk; in dried specimen, the eyes are deep purplish, with a wide pale red-brown outer margin. Head shiny black; bases of antennae and ocelli ringed with greenish. Thorax blackish, shining; lateral sutures (of pleura) pale; anterior portion of mesonotum shaded slightly with greenish. Legs whitish; fore femur smoky. Wings hyaline. Abdominal segments 2-6 hyaline, with faint yellowish tinge. Tergites 7-10 pale brown, ruddier than in P. punctiventris (now a synonym of Plauditus punctiventris); sternites paler, more or less tinged with pale brown. A faint brown line marks the spiracular area. Tails white.

This species is very close to P. dubium, and may prove to be synonymous with it; the color of the eyes in the living insect is the main distinction.

Described as P. dubium

Body length 2.5-4 mm, wing length 3.5-4.5 mm

Abdominal tergites 2-6 of male imago hyaline white, usually with black spiracular markings.

Turbinate eyes almost circular; ruddy brown in living specimens. Thorax shiny black. Legs pale. Wings hyaline. Abdominal segments 2-6 hyaline white; a dark dot over each spiracle, usually a pale hyaline center in each. Tergites 7-10 pale umber brown (piceous, in original description); sternites opaque whitish. Genitalia as in fig. 168.

Start a Discussion of Plauditus dubius


Mayfly Species Plauditus dubius (Tiny Blue-Winged Olives)

Species Range
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