In June, volunteers reported what they believed to be a New Zealand mudsnail in Four Mile Creek, a tributary of Mitchell Creek, which runs to Grand Traverse Bay.
Recent lab results confirmed the sighting: the invasive aquatic snail has begun to colonize yet another Michigan stream.
Heather Smith is a baykeeper with The Watershed Center Grand Traverse Bay. She says the New Zealand mudsnail was first discovered in the state’s inland waters in 2015, in the Pere Marquette River.
Since then, the species has spread to six other river systems: Au Sable, Boardman, Upper Manistee, Pine, Grass, and now, Four Mile Creek.
“They reproduce by cloning,” Smith explained. “So a single snail can result in an entire population very quickly. They have very few natural predators, so when they get into a new water body, they tend to proliferate.”
According to state wildlife agencies, a single female New Zealand mudsnail can snowball into a population of about 40 million snails within a year.
The snails have no known natural predators in Michigan, and their tiny size — 50 to 100 snails can fit into a space the size of a quarter — makes it more difficult to control spread and growth. Smith says researchers have found them hidden in places like boot laces and tread.
If left unchecked, New Zealand mudsnail colonies have the power to fundamentally alter stream ecosystems, including the health of trout populations. Mudsnails outcompete native invertebrates like mayflies and caddisflies, which fish like trout rely on for food.
“There’s the potential for reduced health of fish because there is no nutritional value in the snails, and when fish consume them, they’re just not getting the same nutrients they would if they were eating native macroinvertebrates,” said Smith.
Smith says this recent detection just underscores local environmental groups’ continued advocacy urging people to clean and dry all boating and fishing gear.
“We don’t fully understand all the implications, all of the harm, that these particular snails have the potential to cause,” said Smith. “I think if we can all do our part to decontaminate our gear, not be a vector, and slow the spread, that’s an important step.”
That goes for those who might fish, boat, or float on Four-Mile or Mitchell Creek. But it’s critical after spending time on any body of water, says Smith.
“There are a number of other invasive species that we’re trying to prevent from spreading,” Smith explained. “It’s about this added stress from this invader in these systems that are already distressed from human disturbances and changes in climate.”
Smith says she thinks of preventing the spread of invasive species as a marathon, not a sprint. And that small victories, like ensuring fewer New Zealand mudsnails hitch a ride out of Four-Mile Creek, are something to celebrate.
Read more about New Zealand mudsnails and how best to clean waders, boots, boats, and other gear here.
