Tardigrades, often affectionately known as “water bears” or “moss piglets,” are intriguing micro-animals. These tiny creatures are known for their unique biology and remarkable resilience. A common question about these miniature organisms is whether they can be seen with the naked eye.
What Exactly is a Tardigrade?
Tardigrades are segmented micro-animals belonging to the phylum Tardigrada. They are invertebrates, meaning they lack a backbone, and are considered close relatives of arthropods. The common names “water bear” and “moss piglet” stem from their appearance and slow, lumbering gait, which can resemble a miniature bear or pig.
A typical tardigrade possesses an eight-legged, segmented body. Each of their short, stout legs usually ends with four to eight claws. The name “Tardigrada” means “slow walkers” in Latin, given by Italian biologist Lazzaro Spallanzani in 1776, reflecting their deliberate movement. These organisms are found across diverse environments.
Their Size and Visibility
While some of the largest tardigrade species can reach up to 1.5 mm in length, most commonly measure around 0.1 to 0.5 mm. This means they are generally not visible to the naked eye. To put their minuscule size into perspective, many tardigrades are roughly the size of a period at the end of a sentence.
Their often translucent or whitish bodies make them difficult to spot without magnification. While a very large individual might be glimpsed under ideal lighting, observing any detail requires specialized tools.
Their Remarkable Survival Abilities
Tardigrades are known for their survival capabilities and are often referred to as “extremophiles.” They can enter a suspended animation state called cryptobiosis, which allows them to endure conditions lethal to most other life forms. One specific form, anhydrobiosis, enables them to survive extreme dehydration by losing up to 97% of their body moisture and shriveling into a compact form called a “tun.”
In this tun state, tardigrades can withstand harsh conditions. They have been observed to survive extreme temperatures, from near absolute zero (-272.95°C) to over 149°C. Their resilience extends to immense pressures, enduring up to six times the pressure found in the deepest parts of the ocean. Some species have also survived exposure to the vacuum of space and radiation levels far greater than what humans can tolerate, partly due to protective proteins like Dsup.
Observing These Microscopic Marvels
Since tardigrades are too small for the naked eye, observing them requires a microscope. A basic compound or stereo microscope is sufficient to view them, with magnifications of 20x to 40x for initial spotting and higher powers like 100x or 400x for intricate details.
These micro-animals are found in various moist environments across the globe. Common habitats include damp moss, lichens, leaf litter, and pond water. To collect them, enthusiasts or scientists often gather samples of moss or lichen and then soak them in water. This rehydrates the tardigrades, allowing them to emerge from their tun state and become active for observation.