Tomah Mayfly

Siphlonisca aerodromia Needham, 1909

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Insecta (Insects)
State Protection
Listed as Endangered by New York State: in imminent danger of extirpation in New York. For animals, taking, importation, transportation, or possession is prohibited, except under license or permit. For plants, removal or damage without the consent of the landowner is prohibited.
Federal Protection
Not Listed
State Conservation Status Rank
Critically Imperiled in New York - Especially vulnerable to disappearing from New York due to extreme rarity or other factors; typically 5 or fewer populations or locations in New York, very few individuals, very restricted range, very few remaining acres (or miles of stream), and/or very steep declines.
Global Conservation Status Rank
Imperiled or Vulnerable globally - At high or moderate risk of extinction due to rarity or other factors; typically 80 or fewer populations or locations in the world, few individuals, restricted range, few remaining acres (or miles of stream), and/or recent and widespread declines. More information is needed to assign either G2 or G3.


Did you know?

The name S. aerodromia was given to this insect due to the flaring abdominal flanges reminiscent of airplane wings (Cornell 2006).

State Ranking Justification

This species was collected by B.L. Peckarsky and K.J. Schneider from the Black River in Lowville, New York. There is an historical record (1906) from the Sacandaga River. This rank was assigned due to the small number of extant occurrences in the state.

Conservation and Management

Conservation Overview

The movement of the species from the stream to the inundated floodplain is dependent on predictable seasonal flooding. Alterations of this flow pattern, especially the construction of dams, may contribute to its rarity (Myers et al. 2010).


This mayfly is vulnerable to damming of water and pesticide use.

Research Needs

Additional surveys should be conducted to identify where spring inundated sedge meadow habitat exists. In these areas, surveys should be conducted with a standardized sampling scheme so long-term population monitoring can occur (NYSDEC 2005).



The mayflies are mostly found in a river with areas that are seasonally flooded (including pools and ditches) and containing sedges. Nymphs are found in rivers with broad, sedge-dominated floodplains. This is a dynamic habitat, characterized by a short period of flooding from snow and ice melt during April-May, followed by receding water from the floodplain during summer months. Standing water often remains until May or June as pools, channels, or isolated ponds. Tussock sedge and rushes are typically the dominant vegetation in these habitats. The inundated, decomposing sedge provides shelter, bottom surface, and abundant food.

Associated Ecological Communities

  • Unconfined river (guide)
    The aquatic community of large, quiet, base level sections of streams with a very low gradient.


Identification Comments

Identifying Characteristics

The Tomah Mayfly is large; adults and nymphs range from 15-19 mm in length. Abdominal segments 5-9 are enlarged and median tubercles (small bumps) are found on the underside of the middle (2nd mesothoracic) and last (3rd metathoracic) segments of the thorax. These features are found on both adult and nymph stages of this mayfly (Gibbs et al. 2001).

Best Life Stage for Proper Identification

Adults are rarely observed because they have such short life spans. Larvae are most often dip-netted from rivers. Exuviae can also be identified by experts.


January thru March, the early nymphs feed on detritus in the stream channel and may be found under the ice. During high water, following snowmelt in March and April, the nymphs move from the stream channel to the nearby inundated floodplain. Here they are predaceous, feeding on the mayfly nymphs of the genus Siphlonurus.

Best Time to See

After snowmelt in March or April, the nymphs migrate from the stream channel to the adjacent inundated floodplain. During the last two weeks of May, the nymphs molt to the final stage of larval development. Finally, in late May and early June, they crawl out of the water onto an upright stem or leaf and molt to the winged subadult form. This "hatching" period occurs mainly during the late morning and early afternoon hours, and the population emerges over a period of about 10 days. The newly emerged subadults then fly to the forest canopy along the stream, and in about 3-4 days molt to the final adult stage. The adults live from 1-9 days, during which mating and egg laying take place over the stream in the early evenings. They do not feed as adults.

  • Present
  • Active
  • Reproducing
  • Larvae present and active
  • Eggs present outside adult

The time of year you would expect to find Tomah Mayfly present, active, reproducing, larvae present and active, and eggs present outside adult in New York.


Tomah Mayfly
Siphlonisca aerodromia Needham, 1909

  • Kingdom Animalia
    • Phylum Arthropoda (Mandibulates)
      • Class Insecta (Insects)
        • Order Ephemeroptera (Mayflies)
          • Family Siphlonuridae

Additional Resources


Cornell University. 2006. Threatened and Endangered Insect Abstracts. [online] Available at: <> [Accessed 3 March 2021].

Edmunds, G. F., Jensen, S.L. and L. Berner. 1976. The mayflies of north and Central America. University of Minnesota Press, Minneapolis, Minnesota.

Gibbs, K.E., and T.M. Mingo. 1986. The life history, nymphal growth rates and feeding habits of Siphlonisca aerodromia (Ephemeroptera: Siphlonuridae) in Maine. Canadian Journal of Zoology 64:427-430.

Myers, Luke, Timothy Mihuc, and Boris Kondratieff. 2010. Draft report: Mayflies (Ephemeroptera), Stoneflies (Plecoptera), and Caddisflies (Trichoptera) of the Upper Hudson, Lake Champlain, and Northeastern Lake Ontario watersheds (New York State): A baseline inventory with management considerations for SGCN and other rare and possibly imperiled species.

New York Natural Heritage Program. 2023. New York Natural Heritage Program Databases. Albany, NY.

New York State Department of Environmental Conservation. 2005. Comprehensive Conservation Strategy for Tomah Mayfly. Available at:<>{Accessed 21 June 2021].

Schneider, Kathryn J. 1995. Field survey to Black River Bushes Landing of May 4, 1995.


About This Guide

This guide was authored by: Lutz, Colleen M.

Information for this guide was last updated on: June 2, 2022

Please cite this page as:
New York Natural Heritage Program. 2023. Online Conservation Guide for Siphlonisca aerodromia. Available from: Accessed December 5, 2023.