Sulphurs of the Watauga River

At our January meeting, Appalachian State University graduate student Matt Green answered members' questions about the insect life in the South Holston and Watauga tailwaters.  One topic he covered was the difference between two of the major sulphur species that occur on the Watauga River.  Below is his summary of the differences, as well as some tips on fly sizes and colors to successfully imitate these species.

Ephemerella invaria (The True Sulphurs)

Emergence begins 2-3 days following the mother’s day caddis emergence or overlaps the caddis emergence in the lower Watauga (below the twin bridges), around April 22nd or 23rd until around May 10th. From there, the pattern follows with the trophy section emergence occuring April 28th - May 10th; the Belvins Rd and VFW area occuring May 1st - May 15th (on a good year May 20th), Lover’s Lane are seeing bugs May 10th - May 25th; Hunter Bridge to 19E Bridge happening from May 10th or 15th - June 10 or 15th. The emergence upstream of Hunter Bridge is scant. 

Ephemerlia invaria can come out as early as 1PM and last until 4PM, can occur right before dark ~7PM, or both. Spinnerfall occur over riffles at around 8PM

Late instar nymph: Probably the most important nymph stage for fly fishers, they are solid black with golden or yellow spots and stripes, gray gill plates on the dorsal (top) side of their abdomen, and are 12-15 mm long (size 14 to 16 hook). The thoraxes of these late instar nymphs often appear to be bulging and they eventually split open during emergence exposing a bright yellow thorax and light blue/gray wings.

The second-to-last instar is a bright yellow with dark, grayish blue wingpads.  Having a few bright yellow nymphs can help trigger strikes from fishing keying in on this stage.

Male dun: The larger males (17 to 22 mm) have more slender thoraxes, grayish wings, amber bodies, and large orange, bulging eyes.  

Female dun: Typically a little smaller than the males (14 to 17 mm), have stout thoraxes, light bluish gray wings, yellow bodies, and black, beady eyes. .

A size 16 dry-fly hook is fine for imitating both females and males. 

Spinner: Slightly larger than the duns. The only major morphological differences between the duns and spinners are the development of clear wings, longer forelegs in the males, and longer tails. Spinners are generally 1 to 3 mm longer than duns, and I frequently find that a size 14 hook is easier for both fly fishers and trout to see as daylight fades. Male and female spinners display strong color differences. After molting, male spinners begin with olive-black and olive-gray bodies and lighten to light amber before mating. Female spinners begin with bright yellow bodies and darken to amber before mating.

Ephemeralla dorothea (Little Sulphur)

Emergence begins 10-14 days following the beginning of the true sulphur emergence or overlaps the true sulphur emergence emergence in the lower Watauga (below the twin bridges) around May 8th. The time frame for emergence in the trophy section is May 10th - May 18th, at Belvins Rdand VFW area is May 15th - early-mid June; at Lover’s Lane is May 20th - June 20th, and from Hunter Bridge to 19E Bridge from May 20th - June 20th. Emergence upstream of Hunter Bridge is scant.

Typical daily emergence begins at dusk while the bugs are in the lower river. As the emergence progresses upstream, emergence timing becomes earlier in the day at around 2-3PM and ending around 6PM. Emergence during recreational flows on high water almost always begins between 3 and 4PM and lasts until dark.

Male dun: Pale yellow to cream bodies, light colored cerci (tails), red eyes, size 18

Female dun: Pale yellow body, light colored cerci (tails), black eyes, size 18

While you fish the sulphur emergence this spring and summer, be on the lookout for both of these species and make sure to have flies that will cover the size and color differences noted above.