March Browns and Cahills

Many of America's traditional flies, like the March Brown and the Light and Dark Cahills, originated in the Catskills to imitate the mayflies of this genus. Back then they were classified in the genus Stenonema, the name by which many anglers still know them. Caucci and Nastasi wrote of them in Hatches II:

"There is a matrimony between Stenonema flies and Catskill rivers that is as synonymous as ham and eggs."

A lot has changed in the intervening years. Excepting a handful of species moved to Stenacron, most have been moved to the new genus Maccaffertium. By far the most important species is Maccaffertium vicarium (March Brown & Gray Fox). Of the others in the "Cahill" group, Maccaffertium ithaca is the next most important, along with Maccaffertium modestum and Maccaffertium pulchellum that also produce localized fishable hatches. These lesser species together with a few species of Stenacron and the last remaining species in Stenonema (femoratum) represent the sporadic Light Cahill hatches on evenings in late Spring that often continue throughout the Summer.

Anglers looking for information on the popular species Stenonema fuscum (Gray Fox) should know that it has been combined with Maccaffertium vicarium (March Brown) and is now only considered a lighter and slightly smaller version of the same species.