Why You Need a Marimo Pet (and How to Care for It)

by Patricia Buzo, author of the book A Family Guide to Terrariums

They’re cute, and fuzzy, and entertaining! Keeping one is almost like having your very own pet that you can nurture and watch grow. But exactly what are Marimo moss balls? Are they a plant? A ball of moss? A hairy green alien hamster?

Ready to adopt? Browse our live marimo moss ball terrariums, or read the full marimo care guide.

In reality Marimo “moss balls” (Aegagropila linnaei) are a type of green algae that naturally grows into a spherical shape. They are native to Japan and Northern Europe where they grow in cold freshwater lakes. Over the course of many years, the waves gently roll them back and forth into a perfect ball which can eventually reach up to 8-12” in diameter! The live marimo moss balls that Moss Ball Pets™ offer, called Jr. Moss Balls, are just toddlers coming to you at about 1-2” in size and 6-8 years of age. With proper care, they may even outlive you!

Simply put, you need to have one of these cute little fuzzballs in your life. They are very easy to care for, and keeping one ends up being a little like having both a pet and a plant. You will find yourself booping it on the “nose” as you walk by and talking to it in a baby voice as you do the routine water changes. And they seem to enjoy this treatment! In fact, moss balls like to be rolled around from time to time in order to keep their nice round shape and even green color.

To provide the proper environment for your moss ball, you will need to find a location that receives medium indirect light. It’s important not to put it in a place that receives direct sunlight because they burn easily which results in brown patches of dead tissue. A north facing window or near mild artificial lighting are two appropriate places to house them. Because their native environment is a cold lake, no water heaters are necessary. It’s also a good idea to keep them away from radiators or central heat vents.

Any type of water can be used to house moss balls, even tap water. Personally, I like to use distilled or spring water because tap water tends to leave a hard water ring along the glass as it evaporates, and it can be very hard to remove. Tap water also has a lot of chemicals that won’t necessarily kill them but may keep them from thriving. I do use tap water when rinsing my Marimos, though, and washing out the container.

You will need to replace the water about once every 2-3 weeks. At that time, I usually rinse the substrate and wipe down the inner glass where other types of more undesirable algae may begin to grow. I also run the moss balls under a soft stream of cold water and gently squeeze them to remove any dirt particles that get trapped inside. When you first put them back into the bowl they may float for a day or two but don’t worry, it’s just air that is trapped inside and they will sink again soon.

Prefer to keep yours with fish or shrimp? Our marimo moss ball aquarium guide covers tank setup, lighting, and which tankmates are safe.