These units are the strongest units of the ground Zerg forces.The ultralisks are morphed by the genetic pool of the Ultralisk Cavern.The Ultralisks are superior especially against light enemy ground units like marines,zealots or zerglings.The ultralisks have very strong carapce and also have powerfull blades.Making an ultra army can be a sign of your swarms strength.But its high cost and high technology necessity makes them  difficult units.Ultralisks can not attack air but their anti ground strength compansate this handicap.