Tardigrades, often referred to as “water bears” due to their bearlike appearance, are among the most remarkable creatures on Earth. Though tiny — measuring between 0.3 to 0.5 millimeter (about .01 to .02 inch) long — they have captured the attention of scientists and enthusiasts alike because of their resilience to extreme environments. These microscopic invertebrates are found in diverse habitats, from the deepest ocean trenches to the highest mountain peaks. That they can survive conditions that would obliterate most other life forms makes tardigrades truly extraordinary.

One of the most astonishing feats of tardigrades is their ability to endure extreme temperatures. They can survive in environments as hot as 300 degrees Fahrenheit and as cold as -328 degrees. This resilience stems from a process called cryptobiosis, a state in which tardigrades effectively shut down their metabolism and enter a form of suspended animation. In this state they can withstand extreme temperatures by slowing down all biological processes to the point of near stasis.

Tardigrades also boast an impressive tolerance for radiation. In lab experiments they have been subjected to doses of ionizing radiation that would be lethal to humans. While most organisms’ DNA is damaged under such intense radiation, tardigrades possess a unique set of proteins and DNA repair mechanisms that help them to either protect or rapidly repair damage to their cells.

But their survival doesn’t stop there. Tardigrades can also withstand the vacuum of space. In 2007 they were part of an experiment sent aboard a European Space Agency mission. The spacecraft exposed them to the harsh conditions of outer space — no air, no pressure and unfiltered solar radiation. Remarkably, many tardigrades survived, and some even managed to reproduce once they returned to Earth.

How do they do it? One key to tardigrades’ survival lies in a process called anhydrobiosis. This involves the complete drying out of the body when they lose water. In normal conditions, tardigrades need water to survive. However, in droughtlike conditions, tardigrades can lose up to 95% of their body’s water content and shrink into a nearly indestructible form called a tun. In this form they remain dormant for years, or even decades, until exposed to water again. Once rehydrated, they spring back to life as if nothing had happened.

While tardigrades’ survival abilities are legendary, they aren’t invincible. There are limits to what they can endure, particularly if they are exposed to harsh conditions for extended periods. Still, their endurance makes them a subject of fascination for scientists studying how life might survive on other planets or in extreme environments here on Earth.

Tardigrades are a reminder that even the smallest creatures can be the toughest. While humans marvel at their ability to survive in conditions we cannot imagine, it raises the question of what other life forms might exist in the universe that share similar survival traits.

These tiny, resilient creatures serve as a testament to the diversity and adaptability of life on Earth, illustrating that nature’s wonders often come in the smallest of packages.

Richard Brill is a retired professor of science at Honolulu Community College. His column runs on the first and third Fridays of the month. Email questions and comments to brill@hawaii.edu.