Q. I’ve heard that snails make great additions to ponds. They clean up the muck that collects on the bottom and eat fallen plant litter. Where can I get some and how many should I stock?
A. Whether or not snails will make good additions to your pond depends on the snails. Snails eat plant material. Some like fallen leaves, some like algae growing on pond walls, and others like live plants.
The ability of snails to clean up ponds is greatly overrated. Don’t expect them to reduce the need to mechanically remove debris or do water changes. There is no realistic rule for numbers of snails per pond volume. A few, as curiosities, might be fun.
They are unlikely, however, to remain few for long. Most aquatic snail species multiply rapidly. What seems like a good idea when placing three snails in a small pond can be a nightmare a few months later, when hundreds of offspring have devoured your favorite pond flora.
Snails are also an important intermediate host for several types of internal fish parasites. Introducing them into your pond may unintentionally bring trouble.
Snails can also add interest to a pond. They are one more unpredictable element. You can get snails from local ponds. Check with local fisheries and wildlife authorities for information on local aquatic species. You wouldn’t want to get one that specializes in eating water lilies. Choose only local species.
Most aquatic garden suppliers offer snails for sale. However, I strongly oppose the interstate sale of snails because introducing them into areas where they are not native can have serious ecological effects. Unchecked by appropriate predators and other limiting influences from their native habitats, non-native snails that escape (they always escape) can destroy local vegetation and wipe out native snail species. In turn, other animals that depend on native snails as a food source can be driven to starvation.
Non-native snails can also introduce new diseases and parasites to local waters that will decimate native wildlife. The dangers of introducing exotic species are ever-present in the pond hobby. Well-meaning pond enthusiasts who import non-native species of plants and animals can do far more damage to local wetlands, ponds, streams and wildlife than the greediest land developers.