From Creatures Wikia
The Striker Norns were an aggressive breed created by Arcwelder. They were Magma-based with a strong disdain toward ettins, grendels and adult norns. They were originally made to protect creature eggs and hatchlings, but that often resulted in all other creatures being slain. As they were tested together with the Zabriskie norns, they would attack any adult Zabriskie holding an egg. But as the Zabriskies were tougher, the Strikers in the same world were killed. They're half-breeds, though, rarely expressed this behaviour.