Michigan’s Endangered Species: The Rayed Bean and the Snuffbox

By Annie Perry, MNA Intern

A female rayed bean. Photo: Angela Boyer, USFWS

A female rayed bean. Photo: Angela Boyer, USFWS

Almost one year ago, two of Michigan’s native mussels, the rayed bean and the snuffbox, were listed as endangered under the Endangered Species Act. The rayed bean and the snuffbox aren’t the largest species—both are smaller than 3 inches—but threats to these small organisms can indicate big problems for the environment.

North America has the highest diversity of freshwater mussels in the world, with 300 species found on the continent. Of those species, 38 have recently gone extinct and another 77 are considered “critically imperiled,” according to the U.S. Fish and Wildlife Service. Mussels tend to be long-lived because they can close their shells for protection. As a result, they respond to long-term ecological disturbances rather than short-term disturbances. Some call mussels the “canary in the land mine” in terms of water quality because mussel disappearances show long-term trends that are harming our waterways.

The rayed bean and snuffbox have each suffered significant declines from their original ranges. According to the U.S. Fish and Wildlife Service, the rayed bean, which was once found in 115 streams and lakes, has experienced a 73 percent range decline. The snuffbox has seen a 62 percent decline in occupied streams, but this range decline coupled with population losses show an actual range and population decline of at least 90 percent.

Some MNA sanctuaries contain the rivers and streams these endangered mussels could still occupy, including the Stephen M. Polovich Memorial Nature Sanctuary and the James & Alice Brennan Memorial Nature Sanctuary, both in St. Clair County.

The greatest threat to the remaining freshwater mussels is habitat loss and degradation, much of which is caused by pollution from point and non-point sources. There are some ways you can help conserve the rayed bean, snuffbox and other endangered species in Michigan:

  • Learn more about endangered species and wildlife conservation, especially the endangered species in your area. For information on the protected species in Michigan, check out the U.S. Fish and Wildlife Service or one of our past blog posts on endangered species.
  • Get involved with a conservation organization in your community. MNA hosts regular volunteer days at its sanctuaries, many of which take action to protect the sanctuary’s native and endangered species. For a list of MNA’s upcoming volunteer days, check out our events calendar.
  • Limit use of pesticides or lawn-care chemicals. This will help prevent runoff—a type of non-point source pollution—into nearby lakes and streams.
  • Plant trees and plants to help control soil erosion and avoid runoff into freshwater areas.
  • While boating, follow the rules created to help prevent the spread of exotic pests like zebra mussels. Zebra mussels and other exotic creatures act as another threat to the state’s native mussels.
  • Speak up! The Michigan Department of Natural Resources has a hotline you can call if you see someone illegally hunting, trapping or fishing a protected species.

Snuffbox and Rayed Bean Mussels Requesting Aid

by Hannah Ettema
MNA Intern

When most people hear of mussels in Michigan, they think of the invasive and destructive zebra mussels which first entered the Great Lakes in 1988.

However, all mussels are not bad. Some clean and filter water. And there are two more that need our help.

The rayed bean and snuffbox mussel species, found throughout Michigan and the Midwest, is currently being considered for federally endangered status.


Less than one-and-a-half inches in length, the rayed bean mussel is typically green, yellow-green or brown in color. Slightly larger, the snuffbox mussel can grow to almost three inches and is yellow and yellow-green in color and becomes darker with age.

rayed bean mussel in hand

The Rayed Bean gets its name from its green rays and small size.

Both the rayed bean and the snuffbox are suspension feeders, spending their entire lifetime buried in substrate feeding on algae, bacteria, detritus, microscopic animals and dissolved organic material.

For reproduction, a host fish is necessary. The larvae must become attached to the gills or fins of the appropriate host fish to complete growth and development, without harming the fish.


Generally, the rayed bean mussel prefers sand and gravel in small, headwater creeks.

The snuffbox can be found in small-to medium-sized creeks to larger rivers and lakes also prefers sand and gravel substrates.

snuffbox mussels in hand

Snuffbox mussels

Historically, the rayed bean mussel could be found in 112 streams and lakes. Currently they can only be found in 28. The snuffbox’s habitat numbers have dropped as well from 208 streams and lakes to 74.

The decline of both species can be linked to habitat loss and degradation through impoundments, channelization, chemical contaminants, mining and sedimentation. The arrival of the zebra mussel was also a contributing factor to their decline.

In Michigan, the rayed bean mussel can be found in Black River (Mill Creek), Pine River, Belle River and Clinton River. The snuffbox mussel lives in Grand River, Maple River, Pine River, Belle River, Clinton river, Huron River, Davis Creek, South Ore Creek and Portage River.

Some MNA sanctuaries include those river systems. Coldwater River Nature Sanctuary in western Michigan and Huron River Nature Sanctuary in Southeast Michigan for example, have the potential to have either species of mussel.


These two mussels, among others, act as an indicator of water quality because mussels require clean and pristine water to survive.

“They are kind of like the canary in the coal mine as far as water goes,” said Georgia Parham, public affairs specialist for the U.S. Fish and Wildlife Service, in a press release.

By burrowing in the bottom of riverbeds, mussels also help to stabilize the bottom and sediment.

The status of mussels around the world is far worse than mammals or birds. According to The Nature Conservancy, 16.5 percent of mammals and 14.6 percent of birds are extinct. This compared to the 70 percent of mussels that are either extinct or imperiled.

The public has until January 3, 2011 to comment on a proposal for both species to be listed as endangered.

For more information on the proposal, click here.

To learn more about MNA sanctuaries and the mussels they protect, click here.