The Veleek Swarm was found by the Yeerks on Saturn. It feeds off of energy. The Yeerk empire lost quite a few Hork'Bajir and Taxxons trying to subdue it. They finaly managed to lure it into a force field trap by setting up a transmitter that emitted an attractive form of energy for the Veleek swarm. The force field kept it contained, even with the Veleek draining power from it. The Yeerks modified the Veleek so that it could only feed off of energy from a Bladeships engine pods, but they made it attracted to morphing energy. They planned to use it to capture the "Andalite bandits". It dissolves when expossed to water, as the Animorphs proved, in Megamorphs #1.