Flyfishing Entomology


The Hendrickson Hatch




 (photos courtesy of)



The Hendrickson was chosen to profile because the timing of its hatch is close to the publication date of this online magazine.  For many fly fishers, this will be the first major hatch of the season. 

Taxonomic Placement


Hendrickson is the common name for a mayfly referred to by the scientific community as Ephemerella subvaria (ef-fem-er-ella sub-vary-uh).  It can be found in the East and Mid-West, and is one of (655) mayfly species known to reside on the continent of North American.  The following hierarchy illustrates how taxonomists classify the Hendrickson:


Kingdom:                Anamalia              (animal)

 Phylum:                   Arthropoda          (segmented invertebrate, jointed legs)

  Subphylum:            Hexapoda            (six legged)

   Class:                       Insecta                  (insect, three body regions)

    Subclass:                Pterygota              (winged)

     Superorder:            Paleoptera            (ancient, non-pleated wings)

      Order:                       Ephemeroptera    (mayfly)

       Suborder:                Furcatergalia        (fork-gilled)

        Infraorder:                Pannota                 (fused back)

         Superfamily:            Ephemerelloidae  (crawler)

          Family:                       Ephemerellidae    (spiny crawler)

           Genus & Species: Ephemerella subvaria  (Hendrickson) 


Life Stages


Being a mayfly, the Hendrickson has incomplete metamorphosis.  This means it does not have a pupal life stage, only those of egg, nymph, and adult.  Of course, mayflies are unique in having two winged life-stages, the sexually immature dun (subimago), and the sexually mature spinner (imago).

The Nymph



The Hendrickson nymph is found in a wide variety of streams and rivers.  Classified as a crawler, it is not particularly adept at either swimming or clinging.  When dislodged in swifter water, it remains (more or less) motionless, drifting with the current, until able to regain footing.  This drift behavior can be exploited by allowing a nymphal imitation to dead-drift near the bottom with only an occasional twitch.  When swimming, the thorax is flexed in an exaggerated up-and-down manner, using the abdomen somewhat as a fin.


As can be seen in the above photo, the Hendrickson nymphal body is quite robust, not streamlined like swimmer nymphs, nor flattened like clinger nymphs.  The body is very dark in color, almost black, and is distinguished by paler abdominal segments 5, 6, and 7.  The legs are somewhat feeble in appearance.  Excluding tails, mature Hendrickson nymphs vary in length from 8 -12 mm. (1/3 - 1/2Ē) with the female being somewhat larger than the male.  It has three tails (cerci), with the middle tail being slightly longer than the outer two.  Very fine hairs protrude from both sides of the tails.


Hendrickson nymphs are found in both slow and fast water, but they display an aversion to areas subjected to temperature extremes.  As a result, few are found in cold headwater streams or in warm slack-water stretches of rivers.


When preparing to emerge, the mature Hendrickson nymph migrates to slower current.  It will then make several trips to the surface, employing the earlier discussed exaggerated wiggling motion, before finally escaping its nymphal shuck at or just below the waterís surface. 


The Dun




The Ephemerella subvaria female dun is called a Dark Hendrickson, and the male dun is called a Red Quill.  Or, they may both be referred to as a Hendrickson.  However, independent of what they are called, their bodies are colored somewhat differently.



The dun body varies in color, both by sex, and across the broad area of distribution.  However, it is usually some variety of brown, ranging from tan to reddish brown with a lighter coloration ringing abdominal segment borders.  The wing color is gray, ranging from light gray to slate gray.


When water temperatures reach the mid 40ís, sporadic hatch activity will occur.  However, water must reach the 50-55 degree range to trigger prolific hatches.  This peak hatch activity normally starts sometime between mid-April and early-May, and lasts for 2-3 weeks.  It is best to consult a hatch chart for the local area, which will provide more precise timing.


Peak hatch activity normally lasts for several hours, starting in the early afternoon.  In unusually hot weather, the emergence can be delayed until the sun is off the water.


In cool weather, the dun can be tantalizingly available to trout as it floats a good distance downstream while drying its wings.  With the arrival of warmer weather and more prolific hatches, trout will increasingly feed on the dun, and at times with seemingly reckless abandon.

The Spinner



Hendrickson spinners have a body color that can vary from tannish brown to reddish brown to blackish brown with lighter abdominal segment banding.


The wings are hyaline (sort of cellophane-like) with obvious amber veins.  When the veins are in close proximity, as near the leading edge of the forewing, and in its stigmatic area, that part of the wing appears amber-stained, at least when viewed without magnification.


Male spinners gather to form a mating swarm, and female spinners enter the swarm to select a mate.  After mating, the female either jettisons her eggs a safe distance above the stream, or dips to the water, using the waterís contact with the egg sac to release her eggs.


A spinner fall begins several hours after of the start of emergence, often while the hatch is still taking place.  When this overlap occurs, it may be beneficial to switch to a spinner imitation while duns are still actively emerging.


In cool weather, the spinner fall takes place over a more extended period of time.  In warm weather, the event is more concentrated, and of much shorter duration.  In this circumstance, a good strategy is to fish a dun imitation until trout express less interest, and then quickly switch to a spent-wing spinner.




During a major spinner fall, trout will position themselves in natural feeding lanes at the tail end of riffles or runs.  They can become quite selective to wing position at times, keying on spinners with either semi or fully spent wings.




Many fly fishers have their favorite imitations for the mayfly life stages, and are able to use them with some confidence.  However, if that description does not apply to you, or if you would like to try something different, take a look at the following imitations:


Nymph Imitation




The Hendrickson in its nymphal life stage is nicely suggested by this imitation tied by Jason Neuswanger.  Pay particular attention to the robust body and contrasting dubbing colors, which suggest the lighter coloration of abdominal segments 5, 6, and 7.

Dun Imitation



The extended body dun by Ontario flytyer, Christopher Law, nicely captures the wing and body of the natural, and can be found in the forumís pattern database.


The adult mayfly imitations favored by the author are derivatives of the Comparadun popularized by Al Caucci and Bob Nastasi.  They are easy to tie, donít require expensive materials, and can be used to imitate any mayfly by varying size of the hook and color of the materials used for the deer hair wing, dubbed body, and tails.  Further, they float with the body in contact with the surface film, which can be an advantage in slow water, where trout have time to closely inspect oneís offering. 

Spinner Imitations



The above imitation tied by author represents a female spinner attempting to release eggs by falling to the water with wings upright.



The above poly-wing spinner tied by author is a good choice when trout are keying on spent wing spinners.  It is easily tied and effective.





Hopefully, this article has exposed you to some useful information you didnít already know, or had simply forgotten.  If so, maybe that knowledge can be applied to some advantage when you next fish the Hendrickson, or some other mayfly hatch.


If not, perhaps the article will (at least) remind you of the necessity to restock a depleted fly box; either at your vise, or by visiting your favorite fly shop.


About the Author and Photographer


Roger Rohrbeck is a flyfishing, tying, and entomology enthusiast from the state of Washington.  Following retirement from a 35-year career in information technology, Roger re-channeled his creative energy by developing FlyfishingEntomology.com


Jason Neuswanger generously authorized use of the insect macro-photographs included in this article.  An avid fly fisherman, fly tyer, and photographer from Wisconsin, Jason developed the highly acclaimed Troutnut.com.



The following references contain useful information about the Hendrickson hatch and/or Ephemerella subvaria:


In addition, although it includes only western mayflies (not the Hendrickson), the following reference is recommend to western fly anglers:

Created: 12/20/2005   Last modified: 08/25/2006    www.FlyfishingEntomology.com