A Metaphite is a gigantic grub-like alien organism which grows inside a cocoon for 130 years before emerging.
Metaphites are described as being like a living, breathing nuclear reactor, burning up bio-fusionable reserves and producing high levels of radiation; enough to render the atmosphere of an entire planet inhospitable for other life forms.
Metaphites are used by a race of nomadic aliens called Vexrons to xenoform Earth-like planets and turn them into radioactive wastelands which only the Vexrons themselves can thrive in.
A Vexron agent is tasked with finding a suitable location for and guarding the Metaphite cocoon during its maturation period of 130 years (which isn't terribly long for a Vexron, as they live for nearly a millennium).
- Men in Black: The Series, s03e05, "The Way Out West Syndrome" (1999)