What is the difference between a water bear and a moss piglet? Nothing! Both are common names for a tiny animal officially known as the tardigrade. This special animal can live in just about any habitat on Earth. It can even survive in space!
The tardigrade gets those common names from its long, round body and flattened nose. The name tardigrade means “slow walker.” It was given that name because it moves like a big, lumbering bear.
There are about 1,000 different kinds of water bears in the world. They live in oceans, sandy dry deserts and even the tops of trees. Even though there are many kinds of tardigrades, they aren’t closely related to any other animals. Most animals have at least a cousin or two, but tardigrades only share a prehistoric common ancestor with arthropods, which are animals that have an exoskeleton, like insects or crustaceans. They’re truly one of a kind.
Moss piglet of Illinois
Of all the moss piglets in the world, only one can be found in Illinois, and that is the Milnesium tardigradum. Our local tardigrade prefers to live in the water, clinging to mosses and lichens. Sometimes it also lives in plants in lakes and rivers. Our moss piglet can be found everywhere in the world except the oceans. It prefers fresh water to salty.
You may be wondering why you haven’t seen one of our moss piglets before. It’s because they are microscopic and only grow to be about 0.7 millimeters long. How small is that? Smaller than even the head of a pin, which is about 1 millimeter wide. It doesn’t help that their bodies are see-through. It’s a wonder we know about them at all!
Words to know
Arthropod: An invertebrate animal with an exoskeleton, a segmented body and paired, jointed appendages.
Cuticle: A protective or hard layer.
Lumbering: To move in a slow, heavy, awkward way.
Microscopic: So small as to be visible only under a microscope.
So, what does this almost invisible animal actually look like? Their body looks a little like the caterpillar from “Alice in Wonderland,” but with four segments. Each segment or section has two legs. Their eight legs are missing knees, but they have two claws at the end. They are covered in a clear, soft shell called a cuticle. Any color you might see comes from what they ate for lunch and is now in their stomach.
On their faces, they have eyes that are light sensitive, but they can’t see pictures like a human’s eyes. Their mouth looks like a short, thick straw in the middle of their face. This mouth is only used for eating. They don’t have a nose, so they have no sense of smell. Without a nose and a mouth used only for eating, you might wonder how they breathe. They use their cuticle, or body, to breathe, kind of like an amphibian.
These tiny little creatures may seem cute from our point of view, but they are fierce predators in their watery world. They use their straw-like mouth to suck in even tinier animals. Scientists haven’t discovered any animals that like to eat our moss piglet, so they are the top dog in their habitat.
Small creature, big superpower
Like all creatures, tardigrades can’t live forever. In fact, our tardigrade’s average lifespan is only 40 days. But wait, they have special powers, almost like a superhero!
Even though moss piglets like to live in water and need it to breathe, they stay alive even when the water dries up. Their bodies will dry up too, and when the water returns, they come back to life. They can survive at least five years dried up. Some tardigrades can even survive up to 30 years without food and water. Once the water comes back, in a few hours they become themselves again.
All their special features make living anywhere in Illinois possible. So the next time you’re on a walk and find some moss or lichen, take a closer look to see if you can find any Milnesium tardigradum moving around. Even if you can't see them, they may be there. You may discover you had moss piglets running all around you and you never knew!
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