While traveling with a supply caravan during the war, Metus' group was ambushed by the Baterra. Unarmed at the time, Metus was spared from the assault, and made it to the intended destination of an Ice army outpost. He later realized it was due to his lack of armament that he had been allowed to live.
The Baterra were created to kill every armed combatants no matters which Tribe they belonged. And the Skarll are too naiv to drop their weapons so they never learnt how to aviod the Baterra attacks. And Metus never told the other Agori/Glatorian about this. There must be Glatorian killed by the Baterraduring the Core War, but they could have dismissed they as soilders of the other tribes. The war means loss...
The Skrall-base attack happened on the Bara Magna after the Shattering, and the Skrall knew that the other Tribes didn't really know about them (at that time), so they (eventually) triggered their own extinction by chasing the Baterra. Also, IIRC, the Skrall base-what the Baterra destroyed-was near to the Valley of the Maze, where the Baterra acted as guards, so they just "defended" the maze from the Skrall... And yes, tracked down and nearly killed all of them, because the Skrall didn't put their weapons down to prevent their execution, because of their own tribal-thing. (Stroinus once said, in the Empire of the Skrall?, that "An elite warrior never surrenders his weapon")
It became a bit long, but I hope it's understandable.