I didn’t learn about these pale little mayflies until one late afternoon at our camp on the upper river. I had not intended to fish until later, after the sun left the water, but instead set the time aside to photograph a Payne 204 bamboo rod and Hardy Perfect fly reel that were recently added to my collection. 

It was about 5 p.m. when I laid the rod sections with the attached reel on the grass, getting ready to take the photos. I had set up right next to the river. As I readied my camera, I heard a splash across the river and immediately put the camera down to take a look. That’s when I noticed the beginning of a hatch of very light-colored mayflies, about size 16. As the number of flies increased, trout began to rise all over the pool. 

That’s when the excitement associated with feeding trout dictated that it was time to fish, not take pictures. So I immediately and hastily returned to the car, grabbed my waders and fly boxes, and returned to the river. I quickly identified the flies as pale evening dun; attached a size 16 imitation to my 6X tippet; waded slowly into position and cast to the nearest rising trout.

I don’t know how many trout were brought to net that day. I didn’t keep track—there were likely about six or eight. In any case, it was one of those rare days when everything works. The flies hatched in good numbers, the trout rose and they weren’t picky. 

On another day, a year or two later, Jamie and I caught the pale evening dun hatch again at the same pool. We hooked and landed over a dozen good-sized trout during that hatch. Again, a rare and welcome late afternoon of fly fishing. 

Each year thereafter, we looked forward to the pale evening dun hatch at the end of May and June. For whatever reason, when this species of mayfly is on the water, the trout readily take the duns—which is not the case with many other mayflies. That includes Hendrickson, where trout feed primarily on emerging flies, making angling difficult.

I fished a very long time before witnessing a pale evening dun hatch. That was likely because on most freestone rivers, where I don’t fish much any longer, pale evening duns (as the name implies) hatch right at dusk. 

In fact on the upper East Branch of the Delaware, above the Pepacton Reservoir, Roger and I witnessed a huge hatch of these mayflies one evening, right at dark. We didn’t hook a trout between us during that hatch. That was likely because on freestone rivers, where water temperatures tend to be considerably warmer than tailwaters, pale evening duns leave the water immediately, leaving little opportunity for anglers fishing the dry fly. 

Conversely on tailwaters, pale evening duns ride the water for extended periods, due to the very cold water. That makes them extremely vulnerable to hungry trout seeking an easy meal. Hatches on colder tailwaters tend to be much earlier in the day, with duns appearing as early as 5 p.m. As a result, anglers have a much longer window to fish over emerging files.

In the angling community, a lot of anglers—including professionals—refer to these little mayflies as sulphurs or big sulphurs. They are not. While our little sulphurs are in the same genus, they are much smaller in size and tend to be on the orange/yellow side. Pale evening duns are larger, with a light olive body and large light wings. 

There are actually two different species of pale evening duns, one in the genus Ephemerella and the other in the genus Epeorus. They are so similar in appearance that the only way to quickly tell them apart in the field is by the number of tails. The Ephemerella flies have three tails and the other species has two. In all the years that I have fly-fished, I’ve never found a hatch of the Epeorus pale evening duns.

The fly patterns that I have had success with are pale evening duns and spinners, both in size 16. I use a long shank Mustad, a light wire dry fly hook, for the spinner. The dun is tied with ginger hackle and a body made with pale evening duns super fine dubbing. Wings are not necessary. For the spinner, I tie the same fly and just clip the hackles off the bottom. That way the fly floats flat and imitates the spinner. Trout seem to take each fly quite readily.

So far this year, after two trips to the camp (on May 22 and 25), pale evening dun hatches were sparse. Admittedly, the emergence of this fly in large numbers is more likely to occur toward the end of May and in early-to-mid-June, rather than the two dates noted. In my view, pale evening duns offer some of the best dry fly fishing of the season. So anglers should look for the fly when they are on the river during this time period.