1. Tardigrades are tiny, water-loving animals. They prefer wet environments, and as long as the conditions are right, they can be found all over the world in soils, oceans, and lakes. With body lengths usually less than 1 mm, they are difficult to see unless viewed under a microscope, where their charming appearance becomes quite apparent.
2. Their forms and behaviors have earned tardigrades many different names. Biologist Lazzaro Spallanzani named the animal “il tardigrado,” or “slow stepper,” which refers to its ponderous way of moving. When zoologist Johannes Goeze described one in 1773, he called it a “little water bear,” a nod to its resemblance to a plump, lumbering, ursine mammal (albeit one with four pairs of legs). A third name for tardigrades, because they often reside in the water attached to damp moss, is “moss piglets.”
3. There are more than 1,000 different species of tardigrades, and they have many surprising attributes. They represent their own phylum and are related to arthropods (insects, spiders, and crustaceans) and nematodes (very small worms). They have many other notable features, including beautiful, ornate eggs, and they come in unexpected colors, such as red, green, and yellow. In the soil, they eat all sorts of other organisms that are smaller than themselves, such as fungi, algae, and microscopic animals called rotifers.
4. Tardigrades have been around a long time. Fossils date their existence on Earth to more than 500 million years ago. This means tardigrades have survived the planet’s last five mass extinction events. They owe their longevity to some special characteristics.
5. They are perhaps best known for their ability to enter into a state called “cryptobiosis,” or “the act of hidden life.” To achieve cryptobiosis, tardigrades slowly lose almost all of their water and shrivel down to small, dehydrated forms. This seemingly lifeless little ball is called a “tun.” Given the right conditions, tardigrades can rehydrate and resume active living.
6. Tardigrades are extremely resilient. In their tun state, they can survive extreme conditions, ranging from -130 °C (-200 °F) to temperatures above the boiling point of water! Tardigrades have also survived exposure to outer space, extreme pressure, near-total desiccation, and high levels of radiation. They can emerge from cryptobiosis after enduring immensely challenging conditions, even after years of remaining in that state.
7. Their extraordinary abilities offer us ways to better understand how life thrives in extreme conditions. Often, in such situations, DNA can easily be damaged. Scientists are exploring how tardigrades prevent and repair damage to their DNA. For example, in one species, researchers recently discovered a specific protein that helps protect DNA, and they are investigating whether this ability could be applicable to other organisms.
Thea Whitman is an assistant professor in the Department of Soil Science, where her areas of expertise include soil ecology and microbiology, terrestrial carbon biogeochemistry, and climate change. She is always on the lookout for tardigrades plodding around under the microscope.