Slothiens were once peaceful, caterpillar-like herbivores on an unknown or unspecified homeworld. They possessed urticating hairs (loose hairs covered in tiny hooks or venom that cause skin and eye irritiation, sort of like a biological Fibreglass insulation mat) and made their homes in large nests. Unfortunately for all, this all changed when the Zerg Swarms descended upon them to assimilate them into the nightmarish Hydralisks. Not even their nests were spared, which formed the now-organic basis for the Hydralisk Dens, organic Zerg structures used to decode Slothien DNA to local Larvae. It was the urticating hairs which formed the basis for the Hydralisk's frightening and equally deadly projectile needle spines.