The Hysterias are microscopic predators living in big swarms. They look like tadpoles with big teeth, but as a group they appear as a yellow current.
Living in the waters of the big Stingerfan-forests of Aurelia they communicate chemically and act perfectly together. A Hysteria-Swarm is able to kill and eat everything, from a Mudpod to a Stingerfan, even a Gulphog, because the swarm acts like one organism. They kill their prey by injecting them with neurotoxins and consuming the corpse.
In the cases of larger prey such as Gulphogs, they swarm up to land and bite into the prey's foot. After consuming the prey's body and innards, the Hysteria-Swarm builds itself into a mushroom that bursts into eggs that hatch into more Hysterias.
- Extraterrestrial, a.k.a. Alien Worlds (2005)