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Siphlonisca aerodromia The Tomah Mayfly

Siphlonisca aerodromia was first discovered in 1907 by entomologist C.P. Alexander. The adult specimen was eventually given to J. G. Needham at Cornell University who described it as a new species. The Tomah Mayfly is the only member of its genus and its species name stems from the flaring abdominal flanges reminiscent of airplane wings. This predaceous mayfly is primarly a predator of other mayfly nymphs especially those of the closely related genus Siphlonurus.

S. aerodromia is found in extensive alluvial floodplains carpeted by sedges. During a 1-2 moth period of spring inundation mayflies contribute nearly 90% of the total macro-invertebrate mass. At Tomah Steam, Maine, early instar nymphs feed on detritus and algae beneath the ice. During the high water snowmelt in March or April, nymphs move from the stream to the bordering floodplain and become voracious predators. They emerge synchronously in huge numbers, which makes the unique abiltiy of female Tomah Mayflies to reproduce parthenogenically quite strange.

This mayfly was originally collected from temporary pools along the Sacandaga River in New York. After the construction of the Sacandaga Reservoir in the 1930's the species disappeared from the area. Katherine Gibbs rediscovered it in 1978 at Tomah Stream in Codyville, Maine. Since then the species has only been reported at one location in northern New York but is expected to be still present at 16 locations in Maine and three locations in eastern Canada.

Although it may have had a patchy range, there is historical and scientific evidence to support that S. aerodromia once had a more extensive historical distribution. Before damming of rivers for mills, water storage, and time transport, there were an abundance of streams which had extensive wet meadows throughout the Northeast. Where records exist, these systems are reported to have supported a rich and diverse fauna, and it seems likely that the Tomah Mayfly once survived there as well.

The Tomah Mayfly is especially vulnerable to habitat destruction by damming and overuse of pesticides. In Maine the species is listed as threatened thanks partly to its near-endemic status. Despite extensive surveys of 150 suitable locations, only 16 sites were found to support populations of this rare insect. Thankfully, three of these sites are either partly or wholly under conservation ownership by the state.



Burian, S.K. and K.E. Giibs. 1991. Mayflies of Maine: an annotated faunal list. Maine Agricultural Experiment Station Technical Bulletin 142.

Clemens, W.A. 1915. Mayflies of the Siphlonurus group. Canadian Entomologist. 47: 245-260

Fiance, S.B. 1978. A new locality for Siphlonisca aerodromia (Ephemeroptera: Siphlonuridae) Entomological News 89: 208

Gibbs, K.E. 1980. The occurence and biology of Siphlonisca aerodromia Needham (Ephemeroptera: Siphlonuridae) in Maine, USA> Advances in Ephemeroptera Biology. Eds. J. F. Flannagan and K.E. Marshall. Plenum Press, NY. P. 167-168

Gibbs, K.E. 1991. 1990 studies of Siphlonisca aerodromia: distribution of Siphlonisca in relation to abundance of prey and floodplain vegetation at Tomah Stream; new in collection records for Siphlonisca in Maine; search for Siphlonisca collection records in Eastern Canada. Unpublished Report to the Maine Department of Inland Fisheries and Wildlife, Endangered and Nongame Wildlife Program, Bangor, ME. 23 pp.


Written by: Summer Rayne Oakes, 2004

Updated by: Eric Denemark, 2008

Image credit: Image Credit