Tardigrades, or water bears (sometimes moss piglets) as they are more affectionately known, have risen greatly in scientific and public interest in the last few years. These microscopic creatures have bizarrely cute bodies and faces, as well as some extreme survival capabilities, both of which have gotten a lot of attention in recent scientific news.

Extremely cute, amazingly tough

Tardigrades have captured the attention of the entire world with their depictions as adorable, pink, vaguely bear-shaped blobs who can survive just about anything we can think to subject them to. These fascinating creatures were discovered by Johann August Ephraim Goeze, a German zoologist, in 1773, but didn’t become a popular figure for study until recently. Goeze called the tiny things he’d discovered “little water bears,” and a few years later they were officially named Tardigrada (which means “slow steppers”) by Italian biologist Lazzaro Spallanzani.

Tardigrades have barrel-shaped bodies with four pairs of legs. Newly hatched water bears can be as small as 0.05 mm, the largest fully-grown specimens can reach 1.5 mm, and the average water bear is between 0.3 and 0.5 mm in length. While their bodies are made up of a head and four segments, tardigrades lack certain genes and other features which distinguish a thorax or an abdomen from a head, essentially meaning that tardigrades are made entirely of head regions. Tardigrades are also eutelic creatures, meaning that each individual has the exact same number of cells as every other individual of the same species.

Water bears have no respiratory organs, but simply exchange gasses through their skin. They use a pair of piercing organs, called stylets, to feed on the fluids and cell contents of algae, microscopic invertebrates, and plant cells. Tardigrades grow a multi-lobed brain, most commonly consisting of three pairs of linked neuron clusters. Some species of tardigrades possess compound eyes, and many are covered in a variety of sensory bristles.

Tardigrades are a lot more than just a cute face, however! These creatures can survive in some of the most extreme environments and conditions imaginable. Scientists have discovered various species of water bears living everywhere from hot springs, under layers of ice, on the bottom of the ocean, and on the very top of the Himalayan mountains. This wide range of habitats led scientists to experiment and discover just what water bears can survive, with surprising conclusions. These little creatures can survive temperatures in excess of 300°F for a few minutes, a few days at -300°F, and for decades at around 0°F. Tardigrades can also live in the extremely low-pressure environment of a vacuum and the crushingly high-pressure at the bottom of the Mariana Trench (the deepest place on our planet.) They can survive being dehydrated, irradiated, and exposed to various toxins.

There may even be tardigrades surviving on the moon! Thousands of them were aboard the Beresheet spacecraft, which crashed on the moon in April of this year. While some of the water bears probably survived the crash, scientists don’t believe they will be colonizing the moon for themselves. While they can survive the environment for a time, the lack of water makes thriving on the moon practically impossible, even for the amazingly, tough water bears.

A bear with a belly of gold

Scientists devoted to studying tardigrades are discovering new mysteries all the time. Recently, biologist Rafael Martin-Ledo found a water bear that has a stomach full of something that glittered and glowed under his microscope. This individual with the mysterious diet was found on the bank of the Saja river in Spain. While scientists have no absolute conclusion as to what is glowing in the tardigrade’s stomach, Martin-Ledo has a theory: aragonite. Aragonite is a crystal form of calcium carbonate found in the shells of marine animals. Martin-Ledo thinks this glittery creature may have been ingesting aragonite by eating parts of its own mouth, the piercing stylets, which are composed entirely of this mineral.