Are you suddenly spotting snails creeping up the side of your aquarium wall and you can’t figure out how they got there?

A couple of gatecrashing gastropods in your tank isn’t a disaster. Snails aerate substrates, break down fish waste and clean the tank by gobbling up algae and uneaten fish food.

However, if you’re not careful, these slimy suckers can quickly overpopulate your aquarium. Too many can be a sign your tank needs some maintenance.

Professional aquarist Troy Yarbrough says snails are a particular problem in aquariums with live plants, gobbling up their favorite vegetative food sources. “They can also clog filter intakes and detract from the overall beauty of the system,” he says.

Learn how to get rid of snails in an aquarium and prevent more from taking their place with these expert-approved tips.

How Do Snails Get In an Aquarium?

While some hobbyists deliberately introduce certain snail species, not all are invited.

Yarbrough says unwanted snails are stowaways that usually arrive with new live plants or fish. They even hitchhike on driftwood, gravel and fish feces. They can enter as eggs, babies or full-grown adults.

“Baby snails can be very tiny [the size of a grain of sand] so it’s easy to miss them,” Yarbrough says.

How Do Snails Reproduce?

Even if you only have a single snail stowaway, your tank can still be overrun. That’s because most snails are prolific procreators who fertilize their own eggs. Plus, these fast-growing mollusks can start reproducing at just over a month old, with some species laying dozens of eggs at a time.