Tardigrades, also known as water bears or moss piglets, are microscopic invertebrates known for their resilience. These eight-legged animals are found in diverse environments across the globe, from the deep sea to mountaintops. Their ability to survive extreme conditions has made them a subject of scientific curiosity.
The Actual Size of a Tardigrade
Fully grown tardigrades are between 0.3 and 0.5 millimeters long, though the largest species can reach up to 1.2 millimeters. This means that even the largest specimens barely exceed one millimeter in length.
The size of tardigrades varies across their lifecycle. Their eggs are tiny and spherical or oval, and their dimensions are a fraction of an adult’s. Upon hatching, young tardigrades are considerably smaller than their mature counterparts and must shed their tough outer cuticle multiple times to grow to their full size.
Comparisons to Everyday Objects
An average tardigrade is about the size of the period at the end of a sentence in a standard printed document. A useful comparison is with a single grain of table salt or fine sand, as a tardigrade is roughly equivalent in size. If you were to place one on the tip of a ballpoint pen, it would appear as a minuscule speck.
A person with excellent eyesight might be able to spot a tardigrade as a tiny, whitish dot against a dark background. Seeing their distinct features, like their eight legs or plump body, is impossible without magnification. A simple magnifying glass can make them visible, but a microscope is needed to observe their slow-walking gait and bear-like appearance.
Size in a Microscopic World
Within their habitat, tardigrades are large compared to many other microorganisms. For instance, bacteria are significantly smaller, measuring only a few micrometers in length, and a tardigrade would appear enormous next to a colony. They are found feeding on these smaller organisms, as well as algae.
Compared to larger single-celled organisms, such as amoebas or paramecia, tardigrades are still considerably bigger, placing them in a higher tier of the microscopic food web. To observe a tardigrade clearly, a standard light microscope set to a low power, such as 20x or 30x magnification, is sufficient. This magnification brings their lumbering movements and body structure into clear view.