An escaped mutated beast was featured prominently in the episode "Unleashed". It was primarily composed of Gila monster, rattlesnake, cougar, parasitic wasp, and bat. It had a tail with a rattle and a stinger (ovipositor), which, when used on another creature, "impregnated" it with its larvae.
The larvae would then incubate in the host (dead or alive) for approximately twenty-four hours, stealing nutrients from them in the meantime, after which they would eat their way out (this would obviously kill the host). It made its first cameo re-apparition in Nothing As It Seems and a later on William's Neogenesis simulation in Brave New World - Part 2.