Yesterday I met a scientist from Juniata College in Pennsylvania who studies the small creatures living in natural springs. He samples the life hidden among the stones, leaves, and flowing water—an entire world most of us overlook when we pause beside a spring.
One of the creatures he finds is the planarian, a free-living freshwater flatworm. Planarians are soft-bodied, flattened animals that glide over submerged rocks and other surfaces. Some have a distinct little head with eyespots, and they are famous for their remarkable ability to regenerate damaged or missing body parts. They are predators and scavengers, feeding on very small animals and organic material in the spring’s food web.
The scientist made an important point: the presence of planarians does not mean a spring is polluted. Flatworms are common residents of natural freshwater habitats, including springs, streams, ponds, and cave waters. Like many living things, their numbers and kinds can tell a fuller story only when considered with the water’s temperature, chemistry, oxygen, current, bottom habitat, and the other creatures present.
Planarians also leave a thin trail of mucus, or slime, as they move across rocks and other submerged surfaces. This slippery path helps them glide, but it can also play a role in feeding. Small prey may become entangled in the mucus or be slowed by it, making capture easier. A planarian can then extend its muscular throat, called a pharynx, from the underside of its body to take in food. What seems like an inconspicuous trail on a wet stone is part of a surprisingly effective hunting strategy.
He said that most springs he samples have plentiful large flatworms. But the Warm Springs are different. There, he finds only a small number of smaller flatworms. That difference raises interesting questions. Is the warmer water affecting which species can thrive? Does the mineral content or chemistry of the water favor smaller animals? Is there less food, a different flow pattern, or more pressure from predators? Perhaps the Warm Springs support a distinctive community specially adapted to conditions unlike those in cooler springs.
Springs may look simple—a clear flow emerging from the ground—but each one is a meeting place between groundwater and the living surface of the land. Their small inhabitants can reveal patterns invisible to our eyes.
The next time you visit a spring, look more closely at the wet stones and quiet currents. Somewhere in that clear water, a flatworm may be gliding along, part of an old and intricate community beneath our notice.