Snails are the slow, slimy soldiers slaying sludge in your pond. Pond owners and aquarium keepers alike have turned to these aquatic gastropods as algae-eaters, food for larger animals and even as pets.
But are snails actually a good addition for your pond? The answer depends on the kind of snail.
Egg-laying snails can become pests, reproducing rapidly and clogging pumps. Live-bearing species, on the other hand, are much more polite guests, only giving birth to a few young at a time.
Even live-bearing snails, however, have their limitations – and you should never rely on them as your primary source of algae control. Keep reading to learn more about how best to make use of snails in your pond, and understand what you can reasonably expect from them.
Good for Your Pond: Japanese Trapdoor Snails
Japanese Trapdoor Snails are the only type of snail that you can safely introduce to your pond. While other types of snails reproduce quickly and can clog pumps, Trapdoor Snails are slow breeders that grow too large to work their way into pond plumbing.
Japanese Trapdoor Snails (Viviparus malleatus) gain their name from the fingernail-like plate at the bottom of their shell. When scared, the snail can retreat into its shell and pull the plate – called an operculum – behind it, like a trapdoor.
These snails might look like empty seashells when you receive them in the mail or add them to your pond, but if their trapdoors are still intact, you know the snails are alive and waiting for a safe moment to emerge.
Another trait that sets Trapdoor Snails apart from other species is how they reproduce. While some species of snail can lay 100+ eggs every few weeks, Japanese Trapdoor Snails only give birth to live young. These young develop in eggs inside the mother before hatching internally and emerging as fully-formed, BB-sized babies. This type of reproduction is called oviviviparity, a term meaning part egg-laying (oviparous, like birds) and part live-bearing (viviparous, like most mammals).
What Do Trapdoor Snails Look Like?
Japanese Trapdoor Snails are one of the larger aquatic snails sold for use in ponds, with a mature shell diameter of 2 to 3 inches. They have black or dark brown shells with a hinged trapdoor at the base.
Will Snails Get Rid of Algae?
Algae is a snail’s main source of food, but you shouldn’t expect a few snails to keep your pond completely algae-free.
Many pond owners overestimate just how much algae-control they can expect from their gastropod guests. Snails – even big ones like Japanese Trapdoor Snails – can only fit so much algae in their tiny bodies. And all of the algae they do eat eventually makes its way out of the … other end … of the snail, increasing the overall nutrient load in the pond. You also can’t depend on snails to help with single-cell algae – the stuff that turns water green – because it’s just too small to eat.
The bottom line: Snails will eat some string algae, but you shouldn’t rely on them as your main source of algae control. They can be helpful, though, when used in combination with good pond hygiene and plenty of nitrate-consuming aquatic plants.
A word of caution: Be careful if you use algaecide or copper-based water treatments (like IonGens) or medications in the pond. Snails are extremely sensitive to these substances, and you could end up killing them. (Algaecide also isn’t good for fish, and it doesn’t treat the nutrient issues that cause algae – so we recommend avoiding it even if you don’t have snails.)
What to Expect When Buying Trapdoor Snails
Make sure to buy your snails from a reputable distributor, and make sure that the snails you’ll be receiving are, in fact, live-bearing Japanese Trapdoor Snails. We recommend buying your snails in-person from Splash, or online from The Pond Guy.
Snails purchased from Splash come home with you in a bag with oxygen and water. Online sellers often ship their snails in wet paper. Regardless of how you buy, you can expect your snails to feel a little nervous after transit, meaning they’ll be hiding in their shells.
As long as the snails’ trapdoors are still intact, you’ll know they’re alive. You might also notice algae growth on the shells, or lots of muck in the water or packaging. This is normal (and makes the sludge-loving snails happy.)
Acclimate your new snails to the pond the same way that you would acclimate new fish. Float the bag for a few minutes, then gradually add water from the pond into the bag. Release the snails in a shallow area after about an hour. They’ll make their way to other areas of the pond when they feel safe enough to emerge from their shells.
How Many Snails Will I Need for a Pond?
Most snail breeders recommend a population of at least 10 snails per 50 square feet of pond. If you have a farm pond, you’ll need at least 200 snails to make a noticeable difference in algae growth. (Exact numbers will vary depending on the quality of your filtration and amount of debris in the pond).
Remember, though, that snails should never be your main source of algae control. In addition to adding snails, make sure your pond has lots of aquatic plants, plus sufficient biological and physical filtration. Snails are not necessary for keeping algae at bay – but some people find them useful when used in combination with other methods.
Do Trapdoor Snails Get Along with Koi and Goldfish?
Japanese Trapdoor Snails are extremely docile and get along fine with koi, goldfish and other pond residents. They are also gentle on plants, preferring soft algae over chewy lily pads.
How Often Do Trapdoor Snails Reproduce?
Japanese Trapdoor Snails give birth to live young about twice a year in the wild, and every few weeks in captivity. Each birth results in 3 to 15 pea-sized babies. Of those, usually one or two survive.
While many other types of snails are hermaphroditic (having male and female organs), Japanese Trapdoor Snails are distinctly male or female. The two sexes look almost identical, but males typically have one antenna/tentacle that is larger than the other that acts as a reproductive organ.
Trapdoor Snails are slow in every way – especially when it comes to building their population. They have fewer young than other types of snails, reproduce less frequently, have a longer gestation period (up to nine months) and don’t start breeding until about 18 months of age. All of these traits make them unlikely to take over your pond.
Will Trapdoor Snails Survive Winter?
Japanese Trapdoor Snails will survive winter in most parts of the US as long as the water is deep enough (about 20 to 30 inches). Unlike some other types of snails, Trapdoor Snails have gills that let them remain underwater all winter without needing to surface.
Like fish, snails still need oxygen in winter. Installing an aeration system will help keep a hole open in an iced-over pond so that bad bases can escape.
Other Types of Snails
Japanese Trapdoor Snails are the only snails that we recommend intentionally adding to your ecosystem, but you’ll likely find other species appear naturally over time.
These snails – often a variety known as ramshorns – hitch a ride into your pond via aquatic plants or on the backs of other animals, and they tend to reproduce quickly.
Should I Remove Pond Snails?
You usually don’t need to remove snails from the pond unless they cause problems. Every pond likely has a few small snails hiding in it, and these snails can provide a good source of food for other members of your ecosystem.
On rare occasions, however, they do create issues. Small, egg-laying snails can sometimes take over a pond and make their way into pumps. If you find yourself in this situation, remove as many snails as you can by hand, and clean your pump frequently to prevent damage. (Fun fact: a group of snails is called an escargatoire). Be wary of chemical treatments that could harm not just snails but also fish and other pond life.
Because their population can take off so quickly, you should never intentionally introduce an egg-laying snail to the pond. Stick to live-bearing Trapdoor Snails.