New Zealand mudsnails

The New Zealand mudsnail is an invasive species in the United States, it is native to New Zealand, in 1987 they were found in the U.S, in Idaho. It is believed they hitchhiked on imported gamefish and/or on recreational wading gear from invaded waters. Since then, they have spread throughout the western U.S. and the Great Lakes region. They are a hardy species that can pass through fish undigested, have a large range of environmental tolerances, and can hitchhike on a variety of recreational and commercial aquatic equipment (WI DNR).

In Wisconsin streams, a high density of New Zealand mudsnails leads to a lower density of macroinvertebrates. Macroinvertebrates are important for freshwater health.

Currently, there is little evidence to suggest that mudsnails are leading to reductions in growth rates of the brown trout that consume them in southern Wisconsin; however, it is unclear what impacts they may have in less productive systems or over the long term. New Zealand mudsnails do have predators in their native range, but there is no evidence that predators do or could control populations outside their native range.

There’s not a lot of research in Wisconsin about their effects on the ecosystem, but by reviewing their impact in the western United States, we can predict what issues will arise from their growing population (WI DNR).

One of our stream monitoring teams was measuring water quality and found invasive New Zealand mudsnails in Token creek, a headwater tributary to Lake Mendota, where they had not previously been found. This was the first discovery of New Zealand mudsnails in the Yahara River and Lake Mendota watershed.

This kicked off Rock River Coalition’s partnership with the Upper Sugar Watershed Association and Wisconsin River Alliance to recruit volunteers and monitor at locations in the watershed that are at high risk of being invaded by New Zealand mudsnails. RRC is also working on outreach to prevent the spread of this invasive. Check out our boot brush projects page!