Both hold grudges, and sometimes act on them. Picking a fight with a species as widespread, long-lived, irascible and - when it suited them - single-minded as the Dwellers too often meant that just when - or even geological ages after when - you thought that the dust had long since settled, bygones were bygones and any unfortunate disputes were all ancient history, a small planet appeared without warning in your home system, accompanied by a fleet of moons, themselves surrounded with multitudes of asteroid-sized chunks, each of those riding cocooned in a fuzzy shell made up of untold numbers of decently hefty rocks, every one of them travelling surrounded by a large landslide's worth of still smaller rocks and pebbles, the whole ghastly collection travelling at so close to the speed of light that the amount of warning even an especially wary and observant species would have generally amounted to just about sufficient time to gasp the local equivalent of 'What the fu—?' before they disappeared in an impressive if wasteful blaze of radiation.