Splitting from their ancestor, the crustucillus became much more of a threat to their hosts. They now invade the exterior breathing vents of their hosts, causing respiratory distress. They have a main structure that grows outside the body to photosynthesize, while roots grow off it which extend into the vents to collect blood for nutrients. These can cause violent coughing fits, which rupture the colony, spreading them in the air. This could also slow them down to the point where they are helpless against predators, thus spreading to them. To prevent over-colonization, the parasites engages in chemical warfare until one is beaten into submission and eliminated, typically by the larger of the two.