May 1, 2020 • Forum, Tips

The Sulfur Hatch


Springtime brings warmer water, feeding fish, and emerging mayflies. April and opening day of trout season typically brings emergences that occur in the mid-afternoons, and spinnerfalls that come later in the evening. Often fish are not metabolizing yet, and separating the emergences and spinnerfalls makes it difficult to be on the river for both. However, by late May air temperatures are pushing into the 70’s and water temps are in the 50’s making fish hungry. It’s at this time that the first of the pale yellow mayfly emerges. Ephemerella invaria, commonly called “sulfurs”, begin emerging in mid-May. In Grayling, this first of the sulfur hatches is referred to as the “Light Hendrickson”, a remnant of the days when the hexagenia limbata hatch was referred to as the “Caddis Hatch”. Today, the invarias are more commonly called “sulfurs” because of their sulfur colored bodies.

These pale yellowish-bodied, gray-winged size #16 mayflies emerge in the late evening around 7pm-8pm just as the sun’s warming rays are slipping behind the tree-line on the river. This happens to be warmest time of the day as the falling sun lights up the tiny mayflies emerging from the water and slowly rising into the air over the stream. Sulfurs are numerous in clean, cold Michigan streams, and their numbers fill the air evenings from mid-May through June. While they prefer gravel bottom and fairly fast moving water, they can be found in most sections of typical sand and gravel Bottomed cold, Michigan streams.

Once they emerge, the duns (sub-imago) leave the water and head for the trees where they will molt and become sexually mature (imago). Mature invarias (sulfurs) now have a rusty brown colored body and clear, shiny wings.  They will gather in a comfortable air mass high over the river from 7pm-9pm and mate, males will fall to the water, females will deposit their eggs in the water, and both will die. This activity, referred to as the “spinnerfall”, brings even more trout feeding activity. Imagine the warmest time of the day, calm winds, fading sunlight, lots of bugs, and trout coming out of hiding to say, “Here I am, over here! Throw your fly this way!” What could be better?

In early to mid-June, we start to see a second pale yellow mayfly emerging from the water. Ephemerella dorothea is another sulfur colored mayfly that is, however, a size #18. The dorothea hatch emerges with the invarias: two pale yellow mayflies coming off the water; one size #16 and another size #18. Sounds confusing, but if fish are refusing your size #16 sulfur pattern, change to one that is size #18 and you might have more success.

Once distinct difference between invarias and dorotheas is their color once molted and sexually mature (imago). Dorotheas are a size #18 tan to cream color with clear, shiny wings while invarias are a larger #16 rusty brown with clear, shiny wings. So, using a small aquarium net to collect samples and carefully examining the spinners will help you make the correct fly selection.

Four or five full weeks of pale yellow mayflies filling the air in the warm evenings, surrounded by the quiet solitude of the cold water resource. When the hatch and spinnerfall is finished, it’s still light enough to find your way out of the stream ad back to the car. That’s fishing the sulfur hatch.