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A Flat-headed Mayfly (Spinadis simplex)

Need a main photo for this animal



Wallace's Deepwater Mayfly (Spinadis simplex) A State Endangered Species, the flat-headed mayfly larvae have flattened bodies with broad heads and distinctive single platelike gills with tufts at the base. A. simplex nymphs are 0.24-0.35 inches (6-9 mm) long and yellowish-brown with darker markings and with conspicuous filamentous gill tufts visible dorsally. Two bare tail filaments nearly as long as the length of head and body and the presence of spines or tubercles on the dorsal surface distinguishes this species from most other mayfly larvae. The small adult mayfly is 6-8 mm long with a wingspan of 7.5-9.5 mm. Prefers large, fast-flowing rivers where nymphs live among wood or other solid substrates over sand in deep water.

State status

Status and Natural Heritage Inventory documented occurrences in Wisconsin

The table below provides information about the protected status - both state and federal - and the rank (S and G Ranks) for A Flat-headed Mayfly (Spinadis simplex). See the Working List Key for more information about abbreviations. Counties shaded blue have documented occurrences for this species in the Wisconsin Natural Heritage Inventory database. The map is provided as a general reference of where occurrences of this species meet NHI data standards and is not meant as a comprehensive map of all observations.

Note: Species recently added to the NHI Working List may temporarily have blank occurrence maps.

Documented locations of Spinadis simplex in the Natural Heritage Inventory Database as of July 2015.
Summary Information
State StatusEND
Federal Status in Wisconsinnone
State RankS1
Global RankG2G4
Tracked by NHIY

Species guidance

A guidance document is not available at this time. Use the information from the other tabs and contact local biologists, as needed, to develop management and avoidance strategies.


No additional photos are available for A Flat-headed Mayfly at this time. Please consider donating a photo to the Natural Heritage Conservation program.

Last revised: Friday, June 01, 2018