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.
This specimen is interesting because Heptagenia pulla has not been reported from Washington or neighboring states (Saskatchewan is the closest), yet the distinctive key characteristics are clear.
It keys to the genus Heptagenia because the tarsal claw has a single basal tooth, and the gills on segment 7 have fibrils.
For the species key:
1. The left mandible is planate (fairly straight-edged) whereas the right mandible is angulate (has one sharp turn on the edge).
2. The labrum is much wider than long.
3. There's a thin light-colored streak lateral to the eye on the head.