As fly fishing anglers, we all wait for spring, the beginning of a new trout season and the many insect hatches that will follow. When I taught at the Wulff school, one of my responsibilities was to provide the students with a stream-side short course in aquatic entomology. That course included the collection of immature forms of mayflies, stone flies and caddis flies that were available each week. Those insects were identified as to order and in some cases to species. 

During the lecture, I always liked to emphasize how the life cycle of mayflies was established by the river gods with anglers in mind. 

It’s hard to imagine a more perfect creature for us fly fishers to imitate and fish over. Once a year, absolutely on time to the week, nymphs begin the process of transforming into duns and ultimately spinners. This transformation allows the newly hatched flies to ride the surface,  providing anglers with the opportunity to cast their imitations to rising trout.

Beginning in mid to late April, there is a progression of mayfly hatches, starting with quill Gordon. Those flies emerge around mid-day, although it can happen later. In fact, one day on the Willowemoc on what we call the Rhododendron Pool, I hung around and was rewarded with a good hatch of what my friend Roger called Gordons late in the afternoon. I landed a few nice trout during that hatch because I was patient, the flies hatched and the trout rose.

Quill Gordons are followed by the Hendrickson/red quill hatch. Anglers eagerly await the emergence of these flies because the water has warmed a bit and the trout are more active, with large fish feeding at the surface. 

At the beginning of their emergence, Hendrickson/red quill hatches sometimes overlap quill Gordon.

Hendrickson/red quill hatches begin around 2 p.m., although I’ve seen duns as late as 4 p.m. on chilly days. 

Just prior to Hendrickson, right around 12 noon but on the same day, there will be a hatch of blue quills. These small, dark flies always precede Hendrickson/red quill hatches, and are an indicator that the large more desirable flies will follow. I’ve never observed trout feeding on blue quills, but other anglers have.

Pale evening duns follow, with duns emerging around dusk on freestone rivers and 5 p.m. or later on tailwaters. This is my favorite hatch, because trout rise freely to the duns and to the dry fly. That is not always the case with other mayflies, where trout often feed on the nymphs as they rise through the water column. So the pale evening dun hatch is good for the dry fly angler. 

Little sulphurs, March browns and grey foxes follow. Sulphurs hatch at dusk although they have been known to emerge on tailwaters at 1 p.m., due to the very cold water. March browns and grey foxes begin to hatch in the late morning and are on the water sporadically throughout the day. The March brown spinner fall should not be missed, with spent flies on the water at dusk. Large trout look to the dead flies as an easy meal.

All of these hatches follow an annual progression that leads up to the emergence of a hodgepodge of flies during the first week of June. That includes green and brown drakes, the largest flies of the year; leftover March browns; sulphurs; light Cahills and even Isonychias. There’s also a variety of caddis and stoneflies in the mix.

If I were to plot the sequence of hatches on Catskill rivers, they would follow a typical bell-shaped curve. In the beginning, hatches follow one another one by one, with some overlap. But during the first week of June, the species I mentioned all hatch at the same time, reflecting the peak of the bell curve. 

After the first week of June, hatches begin to diminish, with olives, tricos and a few others as the remaining flies of the summer season. There will be a few more species in the fall, including small olives and Isonychias, along with little yellow quills. The other side of the bell curve.

The fact that several species hatch at the same time during the first week of June indicates that all of the significant hatches ended before low flows and high summer temperatures began to adversely impact aquatic insect populations. I believe this is part of the evolutionary process that these insects went through in order to survive and flourish in Catskill rivers.

So “Bug Week,” as some of my friends refer to the first week of June, is the time when the most and largest mayflies and other aquatic insects are on the water. During this short period, large trout will come to the surface to feed on green and brown drakes and all the other insects that are hatching. To be sure, it’s a spectacle to see all these flies at the same time. Unfortunately, for anglers, there are so many flies on the water, that the trout get full very quickly, so feeding—while intense—can be quite short. 

Regardless, anglers that have the opportunity, to be on a river the week of June 1—“Bug Week”—will observe one of the most amazing events in all of nature.