Stylurus amnicola
Riverine snaketail

Key Characteristics

Adults average 2.1 inches (5.4 cm). The Riverine snaketail is the smallest Stylurus species, but has the biggest club. On top of the thorax is a yellow triangle in between the two yellow stripes. Rearward thoracic stripes are reduced to several interrupted black side stripes. Abdominal segments 8 and 9 have broad yellow side spots that do not reach the edge. Eyes are green, legs are black with yellow hind thighs.

Status and Rank

  • State Status: SC
  • State Rank: S2S3
  • Global Rank: G4


County NameNumber of OccurrencesYear Last Observed
Distribution map for Stylurus amnicola

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.


Lotic - depositional. Overall habitat appears to be clear rivers with moderate current and gravel or sandy benthos. Sediments, primarily silt. Adults appear in river/stream/riparian/floodplain corridor. Males patrol over the middle of the river and the species forages in the undergrowth.

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.


Habitat degradation is a significant threat with the impoundment of rivers, poorly drained roads, channelization, and organic pollution. Timber harvest may increase erosion and silt and cause a decrease in dissolved oxygen as canopy cover is removed and water temperature rises. Also impacted by dredging, invasive plants and animals, pesticides, and herbicides.

Survey Methods

An exuvia survey consists of searching the banks and protruding rocks of rapid streams for the cast skin of dragonfly larvae. Males patrol during the middle of the day and the species forages from perches in the undergrowth in either sun or shade. Reported to forest in thick grass and brush. Males patrol with a fast flight over midstream.

Page Citation

Michigan Natural Features Inventory. 2007. Rare Species Explorer (Web Application). Available online at [Accessed Aug 18, 2018]

More Information

See MNFI Species Abstract


Survey References

Technical References

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