An hydra @ Work

Wow… that was particularly cool… assuming those are in competition with your fish for food
The toxin used by hydra to paralyze its prey is called a hypnotoxin. It's a type of neurotoxin that disrupts the nervous system of the prey, causing paralysis. They have stinging cells called nematocysts that contain the hypnotoxin. When a hydra brushes against its prey, the nematocysts fire tiny barbed threads that inject the toxin into their prey. The toxin then works quickly to paralyze and killing, making it easier for the hydra to capture and consume it.

It's fun to see in the video, how it seems to anticipate the movement of the seed shrimp and catches it by it's antennas. Then the way it still tries to put "something" in it's mouth after it flew away.

The poor seed shrimp was dead before it touched the bottom of the tank after freeing itself.

Most reactions