"If you've never seen an ultralisk...it's bigger than a goddamn tank, and louder, and faster. Tall as four marines in full armor, and long enough that in the jungle you can be fighting the front end before you can even see the back of it coming out of the bush. It's got two pairs of scythes attached where wings might be on a dragon. They're called kaiser blades; I don't know why, but I've seen what they can do. They sweep through marine battle armor like it's tinfoil. You can unload a C-14 at an ultralisk until the barrel melts, and you'll only make it mad. Correction: madder. They're already mad. Ultralisks get out of bed mad and hungry. When they're done slashing you to bits, they stomp on the pieces of you before you're all the way dead."
The ultralisk is a 20 meter long and 5 meter high living battering ram, evolved from the docile brontolith; a creature that the ultralisk now bears little resemblance to. Ultralisks serve as the backbone of the Swarm, possessing an exceptionally thick carapace. Ultralisks are the most powerful ground strain the Swarm possesses and their DNA is the "final viable code" utilized by larvae. An example of their might: a handful of ultralisks were "responsible for the death of an entire Confederate garrison" on Timul IV.
Ultralisks attack using large, bone-like scythes which protrude from their backs. Known as "kaiser blades", these scythes are nearly indestructible. Possessing monomolecular edges, these scythes are able to tear through most substances with ease.
Ultralisks have been submitted to countless genetic experiments. By 2500 at least some ultralisks sported four kaiser blades as opposed to the usual two. By the Brood War, prolonged exposure to vespene gas had resulted in an enhancement to the ultralisks' physical capabilities, among which was the evolution of a more hardened exoskeletal shell and the ability to carry out anabolic synthesis, alterations being made to the glands that produce endorphins and adrenal fluids. Ultralisks have been studied by terrans to a significant extent, Avernus Station and the Castanar space platform serving as examples.