The tardigrade, commonly known as the water bear or moss piglet, is a microscopic invertebrate recognized as one of the most durable organisms on Earth. These eight-legged creatures belong to their own phylum, Tardigrada. Their unique ability to survive conditions lethal to almost any other animal has made them a popular subject in science education and among amateur microscopy enthusiasts. This often leads to the question of how to acquire and observe these fascinating extremophiles.
Availability and Sourcing
Acquiring live water bears is straightforward, with a few primary avenues available to the interested student or hobbyist. The most direct method for obtaining a reliable, clean culture is through biological supply companies, which cater primarily to schools, universities, and research institutions. Suppliers offer living cultures, often the species Hypsibius exemplaris, which is commonly used in laboratory settings. Cultures typically cost between $17 and $35 and are usually shipped in an active state or an inactive, dehydrated form ready for reanimation. This professional route provides a known species and a guaranteed quantity.
Alternatively, the simplest and most cost-effective method is to collect them naturally from the environment. Tardigrades are frequently found in moist terrestrial habitats, particularly in cushions of moss or patches of lichen growing on tree bark, rocks, or walls. Collecting a sample involves scraping a small amount of dried moss or lichen into a container, then rehydrating the material with a few drops of distilled or spring water. This process encourages any dormant water bears to exit their survival state, making them active and visible within hours. This natural collection approach allows observers to find a diverse array of species without purchasing cost.
Understanding the Water Bear
Tardigrades are classified within the phylum Tardigrada and are characterized by their segmented bodies and eight stout legs ending in claws. Most species are incredibly tiny, ranging in size from 50 micrometers up to 1.2 millimeters, meaning they are invisible to the naked eye. Their appeal stems from their ability to enter a state of suspended animation called cryptobiosis.
When environmental conditions become unfavorable, such as desiccation or freezing, the tardigrade retracts its head and legs and expels most of the water from its body, transforming into a dried, barrel-shaped form known as a “tun.” In this tun state, the animal’s metabolism slows to less than 0.01% of its normal rate, effectively pausing its life processes. This mechanism allows them to survive environmental extremes.
Tardigrades in the tun state can survive temperatures as low as near absolute zero and as high as 150 degrees Celsius for short periods. They also tolerate ionizing radiation, surviving doses thousands of times higher than the lethal dose for humans. Furthermore, they endure extreme pressures and can survive exposure to the vacuum of outer space, making them a subject of interest in astrobiology research. A tardigrade can remain in this cryptobiotic state for years before being rehydrated and returning to its active form.
Setting Up a Tardigrade Habitat
Observing tardigrades requires a compound or stereo microscope, as their small size necessitates at least 20x magnification for clear viewing. A stereo microscope is often preferred for initial viewing because it allows for the examination of the whole culture dish. Slides, cover slips, and fine pipettes are necessary for isolating individual specimens for higher magnification observation.
When preparing a culture, use spring or distilled water to avoid chemical contaminants like chlorine found in tap water. The culture should be housed in a shallow container, such as a Petri dish, which maximizes the surface area for gas exchange. Tardigrades are sensitive to heat, so the culture is best maintained at a cool temperature, ideally between 10 and 20 degrees Celsius, in a shaded area.
The culture requires a consistent food source, which for many common species is freshwater green algae, such as Chlorococcum, or the detritus naturally present in moss and lichen. For long-term maintenance, changing about half of the culture water every one to two days helps remove waste and refreshes the oxygen supply. To observe an isolated water bear, a small amount of the culture water containing a specimen can be transferred to a slide and viewed under the microscope.