What’s in Your Watershed: The Tiny New Zealand Mudsnail

By Lauren Woodfill

“What’s a mudsnail?” has become a common question this summer as The Watershed Project’s education team and summer camp students explore Baxter Creek in Richmond. Ominous warning signs plead CAUTION! along Baxter Creek, and many other local urban creeks, hoping to stop to spread of these tiny, invasive snails.

The New Zealand Mudsnail, Potamopyrgus antipodarum, is endemic to – surprise! – New Zealand, and thrives in streams and lakes. The small, 4-6 mm long, aquatic snails are remarkably adaptive and tolerant to a variety of habitats, including areas of poor water quality and siltation, and are euryhaline, surviving in both fresh and brackish water. The mudsnails can even live outside of water for up to 24 hours, and close to two months on damp surfaces. The snails can latch onto many different substrates and vegetation, and can be found across the world including in Australia, Asia, Europe, and North America.

The snails were first found in North American in 1987, and in California in 2000. They might have first traveled from New Zealand with the transportation of live game fish, but now are primary introduced to new habitat by attaching to boots, waders, clothing, boats, and other gear. Since they are so small, it is easy for them to catch a ride to a new location on an unsuspecting host.

Why should we care if the mudsnails are living in our local creeks and waterways? The mudsnails rapidly reproduce and has no known natural predators, and can quickly build up extremely dense populations that outcompete native macro-invertebrates and disrupt the food chain. Mudsnails can reproduce both sexually and asexually, and all the mudsnails in North America are genetically identical females, making them clonal and lacking genetic variation.

According to the California Department of Fish & Wildlife, the tiny snails can eat up to 50% of the food resources of aquatic insects in a stream and cause a large reduction in competing aquatic insect populations and overall aquatic biodiversity. Many of the insects the mudsnails replace are critical food sources for fish such as trout and salmon. While fish can eat the mudsnails, the snails are a less nutritious food source for them and over half of the mudsnails can pass through the fish’s digestion alive and unabsorbed, essentially starving the fish.

For such a tiny snail, they can have a huge impact. Here at The Watershed Project, we are required to follow decontamination procedures on our boots and equipment after spending time in a mudsnail infested creek to prevent spreading them to other bodies of water. You can help too! If you are in a creek or body of water with mudsnails, make sure to scrub boots and gear and let them completely dry before entering another body of water. If possibly, keep separate gear for infested waters and clean water.