New Zealand Mudsnails (MZMS) Invade King County!

New Zealand Mudsnails (NZMS) are invasive to local streams that have no natural predators, parasites, or diseases to counter their population growth in North America. They multiply very quickly and have the potential to become a serious economic and ecological problem for the Puget Sound region. Indeed, local municipalities regularly monitor MZMS populations out of concern for adverse impacts to stormwater infrastructure, as well as effects to native species of fish and other aquatic life.

King County Natural Resources and Parks reports that:

New Zealand mudsnails threaten the health and stability of aquatic ecosystems because they crowd out native species – they reproduce quickly and have reached densities of over 400,000 snails per square meter in parts of the US. They have little or no nutritional value to fish or other species; however, they may be consumed instead of other animals with nutritional value. Some studies have indicated that New Zealand mudsnails can alter the chemistry of streams, disrupt the natural food chain, and drive out native stream insects. Natural resource agencies throughout the West are concerned that these animals could further harm threatened and endangered salmon runs.

Mudsnails are hardy, adaptable animals that can easily and inadvertently spread to new areas by people, pets, wildlife, and equipment. Once they become established in a stream or lake, it is nearly impossible to get rid of them without seriously harming native species present. Further, the costs of mitigating stormwater greatly increases due to the damage these mollusks cause to mitigation measures and damage to infrastructure.

MZMS are very small mollusks. Adult snails have been compared to a grain of rice in length (typically smaller than 6 mm in length in the Western US), the shells elongated with 5-6 whorls. When the tip is pointing up, the shell opening is on the observer’s right. The shell opening has an Operculum, which is a protective cover. Shell color is highly variable and can range from gray to light brown to dark brown. The photo below illustrates the small scale of the NZMS.

The small scale of the NZMS. Image courtesy of King County Natural Resources and Parks

The County has produced an NZMS identification information - shown below - sheet can be downloaded and printed to help with identification in the field. Note that many mudsnails indigenous to the PNW are also quite small and may appear similar to these invasives, so please try to identify species accurately before reporting to WDFW or King County.

As of June 2019, New Zealand mudsnails have been documented within King County in the Thornton, Longfellow, Pipers, Mapes, Kelsey, Mercer Slough, McAleer, May, High School, and Big Soos basins. To date (late February 2020) NZMS have not been reported in Issaquah Creek.

As always, be mindful of safety and the inadvertent transport of NZMS on boots, clothing and equipment.


REFs:

King County, Washington’s “Invasive Animal Species in King County: New Zealand Mudsnails” at ( https://www.kingcounty.gov/services/environment/animals-and-plants/biodiversity/threats/Invasives/Mudsnails.aspx )

Wikipedia "Mollusca" at ( https://en.wikipedia.org/wiki/Mollusca )

Wikipedia "Freshwater snail" at ( https://en.wikipedia.org/wiki/Freshwater_snail )

Wikipedia "Operculum (gastropod)" at ( https://en.wikipedia.org/wiki/Operculum_(gastropod) )