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

  • State Status: SC
  • State Rank: SNR
  • Global Rank: G5Q


County NameNumber of OccurrencesYear Last Observed
Grand Traverse1
Presque Isle3
Distribution map for Physella magnalacustris

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.


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 Inland Lake, Littoral, Benthic, Great Lake, Littoral, Benthic

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.


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).

Page Citation

Michigan Natural Features Inventory. 2007. Rare Species Explorer (Web Application). Available online at [Accessed Aug 17, 2018]


Survey References

Technical References

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