Spring Hatches
by Dean Hansen


Spinner falls of subvaria may be more fickle than the emergences. The spent spinners, floating flush in the water, are also much less noticeable than the obvious duns with their upright wings. Expect spinner activity of subvaria an hour or two after the end of the hatch, and don’t expect hours of activity — the spinner fall may be done in less than an hour.

As the subvaria hatch wanes, two slightly smaller species of
Ephemerella, known as E. invaria and rotunda, take over. These two species are so similar in appearance and activity times that the fisherman can ignore any fine differences between them.

They begin emerging about three to four weeks after the start of the
subvaria hatches. Duns are both smaller (#14-16) and lighter in color than subvaria, but the fishing they offer can be just as outstanding. Their lighter color (dun imitations are tied with light olive brown dubbing) gives them the common name Light Hendrickson. They join subvaria in producing amazing numbers of individuals in a stream: a single square foot of gravel in Michigan’s Au Sable River yielded over 1,200 nymphs of invaria and subvaria.

Light Hendrickson hatches also start later in the afternoon, usually
around 4 p.m., and may continue until dusk. Fishing them is similar to fishing to subvaria: first use a nymph, then an emerger and finally a dun imitation.

As the spring days of May warm to early summer days of June, the Light Hendrickson hatches are replaced by the still smaller and lighter E. dorothea or Pale Evening Dun, Sulfur Dun or Little Marryatt.

The Sulfur Dun is aptly named, with its yellow legs and body. This
calls for a dun imitation tied with yellow thread and pale yellow dubbing on a #16 or even #18 hook. Yes, dorothea is considerably smaller than the other three upper Midwest spring Ephemerella species. Expect “normal” hatch activity to occur from about 7 p.m. to dusk, but remember that cooler weather may lead to a longer emergence starting two or three hours earlier.

E. dorothea spinner falls usually occur over riffles towards dusk and
the spent spinners may be joined by the waning spinner falls of the larger and darker invaria/rotunda species. Be observant to exactly what’s on the Water — here’s where a small net to sample the surface could pay for itself many times over. Trying to pick a floating spinner off the surface with one’s fingers is all but impossible—invest in a net, even if it’s simply a 3” x 6” scrap of window screen.

Dean Hansen has a Ph. D. in aquatic entomology and teaches classes in trout stream ecology and entomology. His column appears regularly in Midwest Fly Fishing™ magazine.

It was a beautiful day in mid-May, and the trout season was less than two weeks old. It was classic dry fly fishing — duns were on the surface at a predictable time of day, and trout were lured from their deep cover to take an imitation on the water’s surface.

Trout fishermen looked forward to the Hendrickson hatch even before Roy Steenrod created an imitation of the female dun of E. subvaria in 1916 and named it in honor of Albert Hendrickson, a Catskill fisherman of Theodore Gordon’s era.

The Hendrickson dun is fair sized (hook #12 or 14); hatches are abundant, widespread and predictable. Hatching activity lasts for three weeks or even longer on the same stretch of stream.

Entomologists have recognized the mayfly genus Ephemerella since 1862. As the number of described species grew to over 80, recent authors have split the old Ephemerella into several smaller, more workable units. Former “species groups” or subgenera are now regarded as full genera, and names like Serratella or Drunella refer to a genus with a more narrowly defined set of characters than the old catch-all Ephemerella.

To Midwest fly fishers, four species of Ephemerella give early, fishable hatches. These are E. subvaria, called the Hendrickson or Dark Hendrickson; E. invaria and rotunda, the Light Hendrickson; and E. dorothea, the Pale Evening Dun or Sulfur.
E. subvaria appears first. Expect Hendrickson duns on the water as early as April 20 in southern Michigan and Wisconsin and southeast Minnesota streams, although the start of the hatch may lag by three weeks in the northern part of Michigan and Wisconsin.

My experience has been to expect duns on the water after 2 p.m., but this could vary with air (and hence water) temperature and cloud cover. Get on the stream by 1 p.m. and use a nymph imitation until the hatch starts.

While duns are making an obvious appearance on the water surface,
however, remember that the nymph is struggling to the surface and beginning to escape from its nymphal shuck while still several inches under water. An appropriate emerger pattern, fished in or just below the surface, could prove far more effective than a surface dry fly.
copyright Midwest Fly Fishing™ Magazine 1999
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