Metatraxi

Metatraxi were an insectoid species.

Biology
Metatraxi had jet-black carapaces which were beetle-like. Their claws were large and similar those of lobsters. (PROSE: Alien Bodies)

Metatraxi ate their own parents on hatching. (PROSE: Down)

History
The Metatraxi were evolved by their own planet, Safenesthome, as a way of fighting back the Grub. They were ideally suited to the planet, as they spent so much time going to other worlds fighting wars that they never used enough of the planet's resources, which was the original reason the Grub had to leave in the first place. (AUDIO: Earth Aid)

In 1989, Raine Creevy, the Seventh Doctor and Ace defeated the Metatraxi in Kafiristan. (AUDIO: Crime of the Century)

The Vancouver was attacked by the Metatraxi while bringing food to Safenesthome. (AUDIO: Earth Aid)

The Krotons went to war with the Metatraxi, during which they devastated their homeworld. One swarmleader was an agent of the Celestis. (PROSE: Alien Bodies)

Culture
The Metatraxi would take their enemies to huge arenas, where they would taunt their enemies to death. This would involve a leading Metatraxi heavily insulting the individual they were taunting, getting incredibly personal and playing on all their darkest fears and personality faults. The Seventh Doctor was subjected to one of these ordeals. (AUDIO: Earth Aid)

Behind the scenes
Originally, the Metatraxi were to be featured in World War, a stageplay by Ben Aaronovitch and Andrew Cartmel that was scrapped and replaced by Terrance Dicks' The Ultimate Adventure. (DWMSE 10)

They were later set to appear in Earth Aid, a TV script written by Ben Aaronovitch for the Seventh Doctor in the cancelled Season 27. In this story, they would have been seen to be forcing their enemies through all methods, particularly bargaining, to take a weapon, as a problem in their mental complex was that they could not harm un-armed opponents. They later appeared in the audio version of the same story which was produced by Big Finish Productions as part of their The Lost Stories range of audio stories.