Mass Effect 2 & Mass Effect 3
Living beyond the Omega 4 mass relay in the Terminus Systems, the mysterious Collector species is glimpsed to rarely as to be taken for a myth by most in galactic society. In reality, Collectors are human-sized insectoid bipeds and can resemble massive winged beetles. They are a terrifying force in the galaxy, responsible for the murder of hundreds of thousands.
Collectors generate permanent stasis fields around themselves, creating nightmarish red-shifted energy fields. In battle, they hold position whenever possible, relying on their aggressive biotics and nearly limitless power. Several types of bipedal Collectors have been identified, including minions, defenders, zealots, assassins and artillery-operators.
Acting together, Collectors have imprisoned entire cities in stasis. While no definitive forensic accounting exists to explain the fate of those imprisoned, leading speculation is that victims are harvested for scientific experimentation and neuro-biological repurposing.