Epeorus suffusus
A mayfly

Key Characteristics

Adult mayflies of the Epeorus genus have a wing length between 7 and 19 mm. The eyes are quite large and, in the male, forelegs are as long or longer than body length. Epeorus nymphs have a generally flattened appearance, with two tales and a body length of 7-17 mm. Head shape is trapezoidal, being wider at the front. The legs are long, with flattened, wide femurs, each typically marked with a single large brown dot on the dorsal side. Plate-like gills are present on body segments 1-7. The thorax of Epeorus suffusus is a dull brown, with the posterior portions of a darker shade. The legs and tails are a pale yellow color.

Status and Rank

  • State Status: SC
  • State Rank: SNA
  • Global Rank: G1Q


No known occurrences in Michigan

Updated 5/15/2018. Information is summarized from MNFI's database of rare species and community occurrences. Data may not reflect true distribution since much of the state has not been thoroughly surveyed.


Epeorus nymphs inhabit areas of rapidly flowing water in cool, shallow streams, where they can be found clinging to rocks or sticks (Edmunds et al. 1976).

Natural Community Types


For each species, lists of natural communities were derived from review of the nearly 6,500 element occurrences in the MNFI database, in addition to herbarium label data for some taxa. In most cases, at least one specimen record exists for each listed natural community. For certain taxa, especially poorly collected or extirpated species of prairie and savanna habitats, natural community lists were derived from inferences from collection sites and habitat preferences in immediately adjacent states (particularly Indiana and Illinois). Natural communities are not listed for those species documented only from altered or ruderal habitats in Michigan, especially for taxa that occur in a variety of habitats outside of the state.

Natural communities are not listed in order of frequency of occurrence, but are rather derived from the full set of natural communities, organized by Ecological Group. In many cases, the general habitat descriptions should provide greater clarity and direction to the surveyor. In future versions of the Rare Species Explorer, we hope to incorporate natural community fidelity ranks for each taxon.


The major threats to mayfly diversity and abundance stem from habitat degradation and compromised water quality. Among the most sensitive of aquatic insect groups, mayfly populations have suffered significant impacts due to stream acidification (Earl and Callaghan 1998, New 1998), the presence of industrial pollutants, and pesticide applications targeting other species (Williams and Feltmate 1992). Minimizing these threats, as well as reducing siltation from run-off and construction projects, will aid in maintaining healthy nymph habitat. As little published information regarding Epeorus suffusus is currently available, further research into the biology, distribution and habitat requirements of this species may illuminate additional management strategies.

Active Period

Breeding from first week of June to fourth week of June

Survey Methods

Adult mayflies can be sampled from mating swarms using a long-handled, fine-mesh nylon net (Leonard and Leonard 1962). There are several methods used to collect nymphs, including substrate sampling using an Ekman or Petersen grab, d-frame net, or naturalists' dredge. Gathering of river stones by hand is another successful method. Collected samples are then rinsed through a series of sieves and specimens hand-picked using forceps (New 1998).

Page Citation

Michigan Natural Features Inventory. 2007. Rare Species Explorer (Web Application). Available online at http://mnfi.anr.msu.edu/explorer [Accessed Sep 24, 2018]


Survey References

Technical References

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