The Silesi are a large, reptilian species. Sociable creatures, they possesse an incredible devotion to any group of which they felt a part. Their crests could change color to reflect their moods. The Silesi language is made of loud, low-frequency noises that they could use to communicate across distances of several kilometers. To compensate for poor eyesight, Silesi have an acute sense of smell. They also tended to possess a formidable knowledge of anatomy, especially nerves, muscles and bone structures, making them dangerous unarmed combatants and skilled warriors, capable of defeating most opponents. When the Fen Domar occupied their world, they used it as a weapons testing ground. This led to the near destruction of the Silesi species. The surviving Silesi escaped to Earth territory.