- The New Zealand mudsnail was found in Bear Creek, part of Thornapple River in Kent County. This an expansion of its range into southern Michigan.
- The snails can reproduce asexually and the Michigan populations appear to be all female.
- The invasive mudsnail can reach high densities, outcompeting native animals and even affecting sport fish like trout.
The New Zealand mudsnail has been found in a new location in Michigan. During a volunteer-based monitoring event, the Coldwater River Watershed Council discovered the teeny tiny invader in Bear Creek, a tributary of the Thornapple River in Kent County. Population genetics will be done to try to trace the source of these individuals.
Once established in a region, the mudsnails are very difficult to contain.
“Unfortunately, their size makes them difficult to detect until it's too late. Once they are in an aquatic system, they are here to stay. We currently have no means of eradicating them or even mitigating their effects,” said Jen Koop, an invasive species biologist and professor at Northern Illinois University.
Mudsnails compete with native snails and other animals for food. They can reproduce quickly and reach high densities. According to the Michigan Invasive Species Program, one snail can clone into 200 snails per year, and in some western states they have reached 300,000 snails per square meter.
“They are super tiny (multiple can fit on the eraser of your pencil) but they have huge impacts. They can drive out native snail species, and in some areas they are so dense that they can clog pipes and drainage systems,” said Koop.
According to Donna Kashian, the Director of Environmental Science at Wayne State University, there has also been a positive feedback loop suggested between the mudsnails and other invasives like zebra and quagga mussels.
“The zebra and quagga mussels are sucking the nutrients out of the water column and putting it on the bottom of the stream, the bottom of the lakes, essentially through deposition of poop and whatnot. And so then it puts this nutrient-rich substrate on the floor. And so the New Zealand mudsnails coming in, it's like this is ideal habitat,” said Kashian.
Great Lakes fisheries are already concerned about reduced water column nutrients, reduced zooplankton that fish eat. This mudsnail is an additional invasive to compound the issue. By outcompeting native organisms, the mudsnail can also affect the entire food web, including sport fish like trout.
“ None of this happens in isolation, and to note that whenever you throw in an additional stressor, there's only so much that the system can take….Because some people may see, ‘Oh, an article on a new invasive.’ It's not that simple. It is an additional stressor on top of the compounding ones that we already have,” said Kashian.
Invasion history and biology
As its name suggests, the snail is native to New Zealand. It has been spreading around the world for over a century. It arrived in the Great Lakes in 1991, most likely through ballast water. This current invasion spread is the first in the southern Lower Peninsula, according to the Michigan Invasive Species Program. The mudsnails have been found in the Great Lakes and several Michigan rivers.
The mudsnail is especially good at invading because it can reproduce asexually and sexually. For species that only reproduce sexually, both a male and female individual have to arrive at a new location to start the spread of the organism. But for the New Zealand mudsnail, it only takes one single individual.
“ If even a single female is transported from one location to the other, she's totally capable of asexual reproduction and establishing herself in a population that just continues to grow. So that is one of the big problems with this particular snail, is its ability to reproduce without a mate,” said Kashian. She said that in Michigan the individuals being recorded are all female.
New Zealand mudsnails have a classic snail shell shape, including a tiny trapdoor to keep them safe. So safe in fact that they can sometimes pass through the digestive system of a fish alive. This means that not only do they survive being eaten, but the fish does not get any nutrients from the meal.
What you can do
To prevent the spread of any invasive species, Michigan’s Invasive Species Program recommends cleaning, draining and drying your equipment in between water bodies. This includes waders and boots, and anything that went near the water or mud. These snails are extremely small and can be hard to spot among any debris.
There is a New Zealand Mud Snail Collaborative that also has information about the animal and how to prevent their spread. The group recommends using different gear for watersheds that are known mudsnail locations. It recommends you clean and inspect all gear before packing it for transport. Freezing, hot water, or long air exposure will also kill the snails and prevent their riding along on your gear to another area.
