The tardigrade, a microscopic invertebrate, is famous for its almost unbelievable resilience, earning it a reputation as one of the toughest animals on Earth. Often called the water bear or moss piglet, this creature can survive conditions that would instantly destroy nearly every other form of life. Its durability has led to questions about where it might be found, including the viral query about whether these tiny animals live on human eyelashes.
Addressing the Eyelash Myth
The definitive answer is no, tardigrades do not reside on human eyelashes. They require a film of water to be biologically active, a condition not consistently met within the dry environment of a human hair follicle. This widespread speculation likely stems from confusion between the tardigrade and a different microscopic resident of the human face.
The actual organisms that inhabit human hair follicles are Demodex mites, eight-legged arachnids related to spiders and ticks. These mites, primarily Demodex folliculorum, are common commensal organisms that live inside the follicle, feeding on dead skin cells and sebum. Both tardigrades and Demodex mites are microscopic and possess eight limbs, which often leads to visual confusion when images are shared online.
Defining the Water Bear
Tardigrades belong to their own phylum, Tardigrada, distinct from insects and arachnids. They are segmented micro-animals, typically measuring between 0.05 and 1.2 millimeters in length, about the size of a grain of sand. They possess a short, plump body with four pairs of unjointed legs, each ending in four to eight claws or suction disks.
The most common name, “water bear,” originates from the German zoologist Johann August Ephraim Goeze, who described them in 1773 as Kleiner Wasserbär due to their slow, lumbering gait. Their nickname, “moss piglet,” references their preferred habitat and stubby, pig-like appearance. The scientific name Tardigrada comes from the Latin meaning “slow walker,” which also refers to their deliberate movement.
Tardigrade Habitat and Distribution
Tardigrades are globally distributed and can be found nearly everywhere on Earth, though not on human eyelashes. They thrive in environments where a thin layer of water exists, such as the moisture film on mosses, lichens, and leaf litter. These semi-aquatic habitats allow them to remain metabolically active, feeding on plant cells, algae, and small invertebrates.
Tardigrades are classified as limnoterrestrial, meaning they are aquatic animals living in terrestrial microhabitats. Their distribution spans from the highest Himalayan mountains to the deepest ocean trenches and the frozen polar regions of Antarctica. Researchers can find densities exceeding two million individuals per square meter in a single cushion of moss. Their ubiquitous presence across all continents is ensured by the ability of their eggs and dormant forms to be transported by wind and water.
The Science Behind Their Endurance
The tardigrade’s fame comes from its ability to enter cryptobiosis, a state of suspended animation, when its environment becomes unfavorable. In the most common form, anhydrobiosis, the animal curls into a desiccated ball called a “tun.” It sheds up to 97% of its internal water content, slowing its metabolism to less than 0.01% of its normal rate.
This metabolic shutdown allows them to endure extremes lethal to most organisms. They survive temperatures as low as -272 degrees Celsius and as high as 149 degrees Celsius for short periods. They can also tolerate doses of ionizing radiation hundreds of times greater than the lethal dose for humans and have survived the vacuum and radiation of outer space. Biologically, this endurance is achieved through the production of protective sugars, like trehalose, and specialized proteins that replace water and prevent cellular damage during desiccation and freezing.