Plants and Animals
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
US Status: No Status/Not Listed
State Status: SC - Special Concern (rare or uncertain; not legally protected)
Global Rank: G4 - Apparently secure
State Rank: S2S3 - Rank is uncertain, ranging from imperiled to vulnerable
Occurrences
| County | Number of Occurrences | Year Last Observed |
|---|---|---|
| Allegan | 2 | 1939 |
| Alpena | 1 | 1925 |
| Barry | 1 | 1957 |
| Benzie | 1 | 2013 |
| Berrien | 1 | 2012 |
| Delta | 2 | 2006 |
| Eaton | 1 | 2021 |
| Gratiot | 1 | 1958 |
| Ingham | 1 | 2021 |
| Jackson | 1 | 2000 |
| Kalamazoo | 1 | 1957 |
| Lenawee | 2 | 2023 |
| Luce | 1 | 1991 |
| Mackinac | 1 | 1991 |
| Menominee | 1 | |
| Midland | 1 | 1997 |
| Montmorency | 1 | 1996 |
| Oscoda | 1 | 1924 |
| Roscommon | 1 | 1939 |
| Saginaw | 1 | 2012 |
| Schoolcraft | 1 | 1991 |
| Washtenaw | 1 | 2015 |
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.
Habitat
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
- Headwater stream (1st-2nd order), riffle
- Headwater stream (1st-2nd order), run
- Mainstem stream (3rd-4th order), run
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.
Management Recommendations
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.
Aerial net, visual survey
Survey Period: From third week of May to second week of September
Time of Day: Daytime
Survey Method Comment: Adults
D-frame net, dip net
Survey Period: From first week of January to fourth week of December
Time of Day: Daytime
Water Level: Low Water Levels
Water Turbidity: Low Turbidity
Survey Method Comment: Larvae
Exuvia survey
Survey Period: From fourth week of May to second week of September
Time of Day: Daytime
Survey Method Comment: Adults/Larva
References
Survey References
- Foster, S.E. and D.A. Soluk. 2004. Evaluating exuvia collection as a management tool for the federally endangered Hine's emerald dragonfly, Somatochlora hineana Williamson (Odonata: Cordulidae). Biological Conservation 118: 15-20.
- Martin, J.E.H. 1977. The Insects and Arachnids of Canada (Part 1): Collecting, preparing, and preserving insects, mites, and spiders. Publication 1643. Biosystematics Research Institute, Ottawa.
Technical References
- Dunkle, S.W. 2000. Dragonflies through Binoculars. Oxford University Press, Oxford. 266pp.
- Mead, K. 2003. Dragonflies of the North Woods. Kollath-Stensaas Publishing, Duluth. 203pp.
- Merritt, R.W. and K.W. Cummins. 1996. An introduction to the aquatic insects of North America, 3rd ed. Kendall/Hunt Publishing Company, Dubuque. 862pp.
- NatureServe. 2005. NatureServe Explorer: An online encyclopedia of life [web application]. Version 4.5. NatureServe, Arlington, Virginia. Available http://www.natureserve.org/explorer