The Kalduu were sapients indigenous to Ropagi II. They were able to stop the Ropagu civil wars. As they lacked vocal cords, Kalduu communicated telepathically. They could form a group mind if two or more Kalduu were within 60 meters of one another. This could be extended to their hosts, which were most often Ropagu, with whom they had a long-standing friendship. They would even bond with the minds of Ropagu leaders. Kalduu ate airborne bacteria as well as germs and viruses from their hosts. They breathed carbon dioxide and exhaled oxygen. Kalduu reproduced by fission.