Spine slugs were parasites which attached themselves to the organic tissue of Skakdi spines. They apparently fed somehow on the energy produced by the host's battle rage. There were theories that the spine slugs somehow encouraged that rage, although nothing was ever proven.
Spine slugs were revolting but harmless creatures. They were parasites that attached themselves to the organic tissue making up Skakdi spines. In some unknown way, they seemed to gain nourishment from the Skakdi's battle rage. Some believed that the spine slugs fed that battle rage, causing the Skakdi to fight and provide more nourishment. Whether or not the spine slugs were to blame for the Skakdi's violent tempers hardly mattered, since the Skakdi would never have admitted it or done anything about it, since it might have cost them their edge in combat.