Rare Mayflies

Tomah Mayfly by Mark McCollough

Mayflies and other aquatic insects may not be the first group of organisms people think of when reflecting on Maine’s wildlife. However, biologists and sportsmen know that a healthy brook trout stream is first and foremost one that hosts robust populations of mayflies, stoneflies, caddisflies, and other aquatic insects.  Maine’s ecosystems are complex and interdependent and when one group of native organisms suffers, no matter how small or unfamiliar, so too generally do other more visible members of the ecosystem. 

Two species of mayflies are currently protected by Maine’s Endangered Species Act. The Tomah Mayfly, listed as Threatened, is a unique insect once thought to be extinct. It was rediscovered in Tomah Stream (Washington Co.) in 1978 and after intensive surveys by MDIFW is now known from about 20 sites in Maine. The nymphal stage of the Tomah Mayfly, unlike other species of mayflies, is carnivorous - preying largely upon other mayfly nymphs. This species depends on highly productive, seasonally-flooded sedge meadows along large free-flowing streams or rivers to complete its life cycle. Although sedge meadows are not an uncommon habitat in Maine, the Tomah Mayfly is found at only a small number of these sites.

Roaring Brook Mayfly, photo by Don Chandler

The Roaring Brook Mayfly is listed as Endangered in Maine. First discovered in 1939 on Mt. Katahdin, this species was not reported again until MDIFW started searching for it in 2003. Found in two small tributaries of Roaring Brook, it was originally believed to occur nowhere else in the world but Mt. Katahdin. Since then, however, the Department has surveyed approximately 160 streams and documented 12 more where the mayfly occurs, bringing the total number of sites currently known in Maine to 14.  All of these sites are clustered in the mountains of central and western Maine. Other researchers have also collected a specimen in the Green Mountains of Vermont and another in the White Mountains of New Hampshire.  While we now know the Roaring Brook Mayfly is not confined just to Mt. Katahdin, or even to Maine, it does appear to be New England’s only endemic mayfly - restricted to cold, undisturbed, high-elevation streams of the northern Appalachian Mountain Range.

In addition to these two listed species, 13 other mayflies are considered Special Concern in Maine. For more information about Maine’s rare mayflies, visit the list of state-listed Endangered, Threatened, or Special Concern invertebrates.     

Support for this work comes from the State Wildlife Grants program (USFWS) and state revenues from the Loon License Plate, Chickadee Check-off and Maine Outdoor Heritage Fund.