Freshwater hydra

The hydra is a tiny pond animal, so small that it is only about the length of a grain of rice — sometimes even tinier. Its body is a slim, see-through tube. At one end it sticks to a leaf or a stone like a little suction cup, and at the other end it opens into a crown of waving tentacles.

Those tentacles are how a hydra catches its dinner. Hydras look gentle, but they are hunters, snapping up water fleas and other tiny creatures that drift too close. Each tentacle is dotted with special stinging cells that shoot out to hold onto passing food. Then the tentacles pull the meal right into the hydra’s mouth.

Here is the most amazing thing of all: a hydra can regrow itself. If a hydra is cut into pieces, each piece can grow into a whole new hydra, tentacles and all. It is almost like magic! Because of this, scientists love to study hydras to learn how bodies heal and how living things fix themselves.

Hydras also make babies in a clever way called budding. A tiny bump grows on the side of the parent, slowly forms its own little tentacles, and then breaks off to drift away as a brand-new hydra. When the pond is warm and there is plenty of food, a single hydra can grow lots of little buds.

Some scientists even wonder whether hydras might not grow old the way other animals do, staying fresh and young year after year. Not everyone agrees, and it is still a puzzle they are studying. Either way, this simple little tube, no bigger than a rice grain, is one of the small wonders hiding in a pond.