Hydra – The Most Dangerous Aquarium Pest

In Greek mythology, the ferocious Hydra was an immortal creature with multiple heads. Every time one of the heads was cut off, two more grew in its place. This arachnid aquarium pest shares a name and a lot of similar features with this mythical beast, making it one of the most dangerous aquarium pests to have in your tank. Hydra are tubular-like creatures that measure about 5 mm in length and are made of epithelial tissues. Between the tissue layers are multipotent stem cells that give rise to four differentiated cell types. The head of a Hydra consists of a mouth and tentacles, and the feet are adhered to the substrate. Hydra do not have organs, but they can elongate or contract their bodies depending on water pressure and temperature. Hydra have no eyes, but they are sensitive to light.

Hydra are predators of the smallest organisms in an aquarium and can cause significant damage by feeding on the live food that many aquarists feed their fish, shrimps or snails. Hydra have stinging cells that can paralyze the prey. This is one of the most effective ways that these aquarium pests kill their victims. They also attack their victims using a sticky substance that is a secretion from the feet.

A hydra has a very low metabolism and only consumes a tiny fraction of its body size each day. In an aquarium, Hydra feed on the smallest organisms such as copepods, rotifers, nematodes, daphnia and bloodworms, as well as on algae. If you feed your aquarium animals with dried conventional foods such as flakes, pellets or algae wafers, the leftovers become the perfect food source for hydra. This is because a hydra can pierce the outer layer of these dry foods and absorb the nutrients within.

To protect your fish, shrimps or snails from Hydra, you can add one of three reported Hydra-eating snail species to the tank: Marisa cornuarietis, common pond snail or Asolene spixi. Unfortunately, these snails can also wipe out the populations of your aquarium plants. If you decide to add a Hydra-eating snail to your aquarium, make sure that it fits with your aquascape.

Hydra is not super mobile and tends to stay in a single place. They can, however, move around the aquarium if they find the environmental conditions better than where they are located. To get to another spot, they release a foot from the end of their body and create a gas bubble that they use as a float. They can then cling to the surface and rise up to a new area.

A common way to prevent the growth of a Hydra population is to shade the aquarium and/or add a piece of glass on top of the aquarium to block out any direct light from reaching the hydra. This can significantly reduce the number of hydra in an aquarium. It is best, however, to take preventive measures before the Hydra problem gets out of hand in the first place.