A Hendrickson Female Dun
The genus Ephemerella is another group of bugs that can be quite the big deal here in the east. In fact the species subvaria is a very big deal. The subvaria hatch is the first “super hatch” of the year and trout are known throughout the east and midwest to go bananas when these things start coming off. To my knowledge and based on my research there are nineteen different species of Ephemerella. The most important species to anglers will be definitely be Ephemerella subvaria otherwise known as the Hendrickson which is named after Albert Everett Hendrickson of Scarsdale New York who was a good friend of Theodore Gordon. In the west the Ephemerella species will be Ephemerella dorothea, and infrequens otherwise known as the Pale Morning DunThe most common name for subvaria is the Hendrickson. They also go by Dark Hendrickson, Red Quill, Lady Beaverkill, Beaverkill, Borcher Drake, and Whirling Dun.
A Hendrickson Male Dun

These little guys begin hatching in the spring, which using us a guide for the hatch, it usually happens in mid to late May or when water temps reach between 50 and 55 degrees. This is arguably the best hatch of the year and when it’s happening the fish are really keyed onto them. The nymphs hatch by swimming or undulating their body to the surface and emerging from their shucks in the film. Once hatched the duns are known to ride in the current for a long time before they take flight which makes them an ideal food source. It’s said that before an emergence the nymphs are extremely active for several weeks which can make the fish put on their feed bags big time before the duns even show up.

The spinners are believed to lay their eggs on the water surface en masse by releasing their egg sack from the oviduct or tail well above the water surface although sometimes they will hover low enough to deposit their eggs in the film. The spinners return to the water for egg laying based on temperature and in most places that means afternoon to dusk where in the midwest it is said to occur in the morning due to the warmer temperatures. Fishing spinner falls can be very exiting depending on the water type. Faster moving streams provide furious action for 20-30 minutes during and after a spinner fall so its important to be ready where slower river or slower sections of rivers offer more prolonged action. This is based on the availability of the spinners to the trout on the waters surface.

The Hendrickson can be imitated easily in a size 14-18 with 14 being the norm around here and 16 being the norm on most other waters. The duns are a pinkish brown to bark brown color with a grey-blue wing. They have very distinct secondary wings and three short tails and are often seen sporting yellow egg sacks. The spinners tend to darken up a bit to a rusty color and their wings do turn translucent like most other species. The rusty spinner is believed to be derived from this species although it is an effective imitation of the spinner for a variety of mayfly species.
Hendrickson Spinners
The nymphs have a short stout appearance with six legs that are barred or mottled and several of the rear abdomenal segments or “termites” are lighter in color than the rest of their bodies. The nymphs are known to be active swimmers and can be a much more effective imitation of the species, especially on colder days.
A Hendrickson Nymph
CDC Hendrickson Compara Dun
CDC Biot Rusty Spinner