One hydra can have anywhere from four to twelve tentacles. Each tentacle has tiny bumps, called nematocysts. The nematocysts release a material that paralyzes
another animals. Hydras use their nematocysts to capture prey and for protection.
Green Hydras use a sticky body fluid at their base to attach to an object in a place where there is a lot of food swimming by. Sometimes they attach to the surface of the water and hang down.
Prey of Green Hydras include aquatic insects, crustaceans (such as water fleas and scuds), flatworms, aquatic worms, fish fry, and other small creatures. They also eat a certain type of algae, called Chlorella, which is what makes hydras green. Chlorella stays alive inside the hydra. The hydra lets the Chlorella make food for it.
The way Green Hydras reproduce is by budding. Budding starts with a small bump on a hydra's body. The bump continues to grow until there is a stalk. Next, the new stalk grows tentacles. When it is ready, the new hydra pinches itself off from its parent.
With the right temperature, and a good food supply, a healthy Green Hydra can make a new bud every three or four days. The population is at its greatest in late spring and early summer. Predators of hydras include flatworms, crustaceans, and aquatic insects. If a hydra needs to move (perhaps it's not getting enough food), it can detach itself and move like an inchworm. Green Hydras are helpful since they control populations of insects (including mosquitos). They must have good water with lots of oxygen to live, so when we can’t find them, it’s a sign that water may not be healthy.