Nature Nearby: The toughest critter in Hyattsville — or anywhere else
By Fred Seitz
I was out hunting in the moss, and there he or she was.
I looked closely with my illuminated magnifier and saw the little dark shape creeping through the wet moss. While the magnification was not sufficient to see his eight legs, I am reasonably certain it was a tardigrade, or slow-stepper, named for the way they walk. They’re also known as water bears or moss piglets because of their appearance and need for wet surroundings.
These minute little beasties are by no means solely Hyatsvillians, as they can survive just about anywhere on earth — and beyond, as you’ll soon see. There are 1,300 species inhabiting mountains (including Mount Everest), tropical jungles, hot springs and oceans worldwide. They can even survive in Antarctica.
Based on fossil finds, we know that tardigrades have been around at least from the time of the dinosaurs, but they likely evolved long before T-Rex and his associates arrived. The earliest fossils were found in amber and differ only slightly from their descendants, having one less pair of legs.
Tardigrades are usually about 0.02 inches long, have eight legs, and are black, brown, or orange. Their coloring is at least partly attributable to what they eat. They munch on moss and algae, and also eat small nematodes, which are very small worms that live in water or moss. Larger nematodes eat them, and sometimes tardigrades eat other tardigrades.
Tardigrades adapt well and can survive in adverse conditions. They’ve survived being dehydrated, frozen, exposed to radiation and even subjected to the complete lack of oxygen in outer space. Some have visited the space station, and others were on board an Israeli space probe that crashed on the moon. Sadly, we don’t know how the crash victims fared, but the other eight-legged astronauts who visited the space station did return, and several of them survived.
Tardigrades sometimes survive by entering a cryptobiotic state, an inactive condition triggered by a dry environment. This allowed them to survive the airlessness in outer space. When conditions become more favorable, rehydration wakes them from dormancy.
Some tardigrade species can reproduce parthenogenetically — without a mate — while others partner to reproduce. In some tardigrade species, males deposit sperm inside the cuticle of a molting, egg-carrying female. Sometimes reproduction occurs after molting, as females deposit eggs in their shed cuticle, which are later fertilized later by males. The young hatch in approximately two weeks, although it can take as long as 90 days depending on species and environmental conditions.
Tardigrades amazing adaptability to a wide variety of settings and hostile conditions make them a focus of a lot of current research on environmental adaptation.
They benefit us in many other ways, as well. Their consumption of small nematodes helps gardeners, as the nematodes often can destroy or damage crops or other plants.
Many people think they’re cute, and some kids raise them in school classes or keep them as pets. There are several delightful videos about tardigrades online, and some very readable books about them — consider starting with Michael W. Shaw’s Kids and Teachers Tardigrade Quiz and Fact Book.
Better still, if you’re up for an adventure, grab a good magnifying glass and head out in search of some moss or leaf litter, and be on the lookout for this minuscule bear, this minute piglet, with a toughness and tenacity far beyond her size. She and her neighbors could give you quite a show.