They lived underground on the planet Ka'Dedus IV, mining the various metals in the planet's crust and outer core. Because of their knowledge of mining and ores, Defels were known to be excellent metallurgists. Because of their ability to "hide" in normal light, Defels were also known to be excellent hunters and thieves. They could see equally well in the dark and in ultraviolet lighting, and their eyes appeared to glow red in normal light. In bright, normal light, however, a Defel was more or less blind. Those Defel who travel off-world during the daylight hours wore special visors to protect their eyes.