Plants and Animals

Physella magnalacustris Great Lakes physa

Key Characteristics

The solid, ovate shell of the Great Lakes physa is medium-sized (to about .8 inches long), moderately glossy and tan to brown in color. The 5 whorls are finely striated and without indented sutures. The large rounded body whorl lacks a shoulder. The aperature is quite long and of a teardrop shape. The snail itself has a dark black head and foot region and long, slender tentacles with eyes located at their inner base.

Status and Rank

US Status: No Status/Not Listed
State Status: SC - Special Concern (rare or uncertain; not legally protected)
Global Rank: G3?Q
State Rank: SNR - Not ranked


CountyNumber of OccurrencesYear Last Observed
Arenac 1 Historical
Benzie 1 Historical
Charlevoix 2 2015
Crawford 1 1939
Delta 1 Historical
Emmet 1 1988
Grand Traverse 1 Historical
Huron 1 Historical
Mackinac 1 Historical
Presque Isle 3 Historical
Roscommon 1 1939

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.


The Great Lakes physa occurs in shallow water along the rocky shorelines of large lakes (Burch and Jung 1992).

Specific Habitat Needs

Cobble substrate needed in: Great lake, littoral, benthic; Inland lake, littoral, benthic.

Natural Community Types

  • Great lake, littoral, benthic
  • Inland lake, littoral, benthic

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

As the Great Lakes physa inhabits rocky shorlines, intense human disturbance and alteration of lakeshore habitat should be avoided. Heavy metal and chemical pollution from pesticide treatment (Kosanke et al. 2004), agricultural and residential stormwater runoff, and industrial waste is lethal to many species, even in low concentrations (Besser et al. 2007, Johnson 2009). Acidification of waterbodies decreases available calcium and can result in thin-shelled snails, increasing vulnerability to predation (Brown 1991). Waters with a ph below 5 are incapable of supporting any aquatic snail life (Okland 1992).  Management efforts to reduce pollution and degradation of waterbodies will benefit all aquatic snail species.

Active Period

Active from first week of June to first week of October

Survey Methods

There are several effective methods for conducting aquatic snail surveys. Areas of coarse cobble substrate are best surveyed with a glass-bottomed bucket or scuba search, and hand collecting. Stones and sunken pieces of wood can be picked up, searched, and replaced. Dip net suveys are employed at soft substrate locations. Aquatic vegetation held over a bucket and vigorously shaken to remove individual snails is another technique (Groves 2007).

D-frame net, dip net

Survey Period: From first week of June to first week of October

Time of Day: Daytime

Glass-bottom bucket less than waist deep water

Survey Period: From first week of June to first week of October

Time of Day: Daytime

SCUBA greater than waist deep water

Survey Period: From first week of June to first week of October

Time of Day: Daytime

Shaking vegetation survey

Survey Period: From first week of June to first week of October

Time of Day: Daytime


Survey References

  • Groves, K. 2007. Aquatic Spring Snail Survey and Habitat Analysis. USDA Forest Service.

Technical References

  • Besser, J.M., D.L. Hardesty, I.E. Greer, C.A. Mebane, D.R. Mount, and C.G. Ingersoll. 2007. Sensitivity of freshwater snails to contaminants: chronic toxicity tests with endangered species and surrogates. U.S. Geological Survey.
  • Brown, K.M. 1991. Mollusca: Gastropoda. Pp 285-314. In: Thorp, J.H. and A.P. Covich (eds.). 1991. Ecology and Classification of North Amercian Freshwater Invertebrates. Academic Press, Inc., San Diego, CA.
  • Burch, J.B. and Y. Jung. 1992. Freshwater snails of the University of Michigan Biological Station area. Walkerana 6(15).
  • Johnson, P.D. 2009. Sustaining America's Aquatic Biodiversity: Freshwater Snail Biodiversity and Conservation. Virginia Cooperative Extension Publication 420-530.
  • Kosanke, G.J., W.W. Schwippert, and T.W. Beneke. 1988. The impairment of mobility and development in freshwater snails (Physa fontinalis and Lymnaea stagnalis) caused by herbicides. Comparative Biochemistry and Physiology Part C: Comparative Pharmacology 90(2):373-79.
  • Okland, J. 1992. Effects of acidic water on freshwater snails: results from a study of 1000 lakes throughout Norway. Environmental Pollution 78(1-3):127-30.