This story is about the little sulphur May fly, Ephemerella dorothea, and all of the frustration it seems to create for Catskill anglers. But before I tackle that dilemma, it would be good to discuss all the flies that are called sulphurs. Each year in early June, anglers that check websites provided by local fly shops will find references to hatches of size 14 and 16 mayflies dubbed “sulphurs.” Here’s the scoop. There is only one true sulphur mayfly, indigenous to the Catskills: it’s E. dorethea, the little cousin of the Hendrickson E. subvaria. The other flies called sulphurs are actually pale evening duns. They are larger, lighter in color, with a pale dun wing and greenish bodies. One species is E. invaria, cousin of the Hendrickson; the other, Epeorus vitreus, is a cousin of quill Gordon.

Invaria can be distinguished from vitreus by the number of tails. Invaria, like all Ephemerella mayflies, has three tails; vitreous has two. Call them what you will, but in the hierarchy of entomological classification, they are pale evening duns, not sulphurs. Our true sulphur is a size 18 for the female, about a size 20 for the males. The males have large red eyes. Under normal stream conditions, and by that I mean freestone Catskill Rivers, emergence is at dusk with duns leaving the water quickly, providing trout with little time to surface feed. Emergence on colder tail waters is another story altogether. In recent years, angling friends and I have found sulphur hatches, and very large ones at that, about 1 p.m. on bottom-release rivers. We believe that the colder water temperatures associated with those rivers cause this change in hatch times.

It is my view, having listened to anglers over many, many years, that no insect elicits more consternation than a hatch of sulphur mayflies. In fact, my longtime friend Bill Dorat was so miffed and fascinated by this hatch that he had at least 10 different imitations of the sulphur dun. And every year, about the time sulphurs were expected, discussion about the best patterns along with how trout react to this fly began in earnest.

 So why do sulphur hatches cause so many problems or alleged problems for fly fishers? First of all, sulphurs, like some other species of mayflies, hatch near the bottom and rise through the water column as winged adults. The wings unfold when the fly reaches the surface. As a result, trout pick off a lot of the struggling duns as they make their way to the surface. Many times, they take them just before the insects pop out, creating a disturbance that looks just like a true rise. So in order for anglers to be successful during a sulphur hatch, he or she needs to confirm whether fish are actually taking duns off the surface, or taking emerging flies on their way to the surface or just under or at the surface.

If trout are feeding on emerging flies, casting a dry fly will be all but useless during a sulphur hatch. If this is the case, anglers that swing a Little Marryat wet fly in front of trout feeding on hatching flies may have some success. The same may be said for anglers that are adept at fishing emerger patterns.

What if you find trout taking sulphurs off the surface, make cast after cast with a decent imitation, but it still goes untouched? Make sure that your imitation is a lightly dressed size 18 or 20, and the tippet is 7x. Then pick a steady riser, keep casting and trust that persistence will pay off.