Water bears, also known as tardigrades, are microscopic creatures known for their unusual appearance and remarkable resilience. They are not typically observable without magnification.
Are Water Bears Visible to the Naked Eye?
Most water bear species measure between 0.1 and 0.5 millimeters in length. While the largest might reach up to 1.5 millimeters, appearing as a tiny speck, their translucent bodies make them even harder to spot against most backgrounds.
The Incredible Biology of Water Bears
These organisms are classified as micro-animals belonging to the phylum Tardigrada, making them distant relatives of insects and crustaceans. Water bears typically have a short, plump, and barrel-shaped body, usually segmented. They possess eight stubby, unjointed legs, each ending in a set of four to eight claws or sticky pads. Their bodies are covered by a tough outer layer called a cuticle, which they shed periodically as they grow. They utilize a specialized mouthpart, known as a bucco-pharyngeal apparatus, to pierce cells and extract nutrients.
Water bears are found in diverse habitats across the globe, from the highest mountains to the deep sea. They commonly inhabit moist environments such as damp moss, lichens, leaf litter, and various soil and aquatic sediments. Despite their widespread presence, water bears require a thin film of water around their bodies to remain active and conduct essential life processes like gas exchange.
Unveiling Water Bears: What You Need to See Them
Microscopes, either dissecting (stereo) or compound models, are the primary tools for viewing water bears. A low magnification (20x to 40x) can help in locating them, while higher magnifications (100x to 400x) reveal their intricate details and movements.
To find water bears, samples can be collected from common moist areas like moss growing on sidewalks, roofs, or tree bark, as well as from lichen or leaf litter. Once collected, the samples should be soaked in a small amount of water for several hours to rehydrate any dormant water bears. A small drop of this water is then transferred to a microscope slide using a pipette for observation.
The Secrets of Water Bear Survival
Water bears can survive conditions lethal to most other life forms, often through a state called cryptobiosis. During cryptobiosis, they suspend their metabolic activities to an almost undetectable level. One common form of this survival strategy is forming a “tun,” where the water bear retracts its head and legs, curling into a dried, barrel-shaped ball, losing up to 97% of its body water.
In this tun state, water bears can endure extreme temperatures, ranging from lows near absolute zero at -272°C (-458°F) to highs of 149°C (300°F). They can also withstand immense pressures, up to six times that found in the deepest parts of the ocean, and survive exposure to high levels of radiation, sometimes thousands of times greater than what is lethal to humans. Furthermore, water bears have demonstrated the ability to survive the vacuum of outer space. Their resilience is attributed to protective molecules, including intrinsically disordered proteins (such as CAHS proteins) that form a glass-like matrix to safeguard cellular components, and the Dsup protein which protects their DNA from damage.