Behemoth

Behemoths are "the largest space faring creatures in the chartered galaxy." Immense and docile creatures and bearing resemblance to manta rays, behemoths travel through space, even between star systems, using their own energy.

Behemoths drifted through the void of space, gaining air from the atmosphere of planets. However, they were incorporated into the zerg gene pool when they passed close to Zerus, lured in by the psychic beacon of the Overmind. The zerg developed resistance to vacuum exposure from them, which gave the zerg the ability to travel through the vacuum of space. The zerg exploited this ability to attack the xel'naga worldships and escape from Zerus.

Even after the departure, behemoths still played a role within the Swarm, able to carry overlords and other zerg breeds in the folds and pockets of their sprawling bodies and act as transports, notably when transporting the Kukulkan Brood from Char to Bhekar Ro.