The first Ultralisks encountered on the field seemed to suffer balance issues, and were easily toppled by artillery fire or loss of limbs. Recent reports of sorties with unstoppable Ultralisks have revealed substantial additions to their internal structures: a complex sensory system, an auxiliary nervous system, and specialized muscle fibers that expand or contract in reaction to stimuli. Though these evolutions hint at why a charging Ultralisk can maintain speed with its hind legs severed by a 180mm Crucio shell, they offer very little in the way of new solutions to the Swarms deadly siegebreaker.