The Rachnis are an enigmatic race that are native to the moons of Jupiter
They are most well known for their odd trade requests for which they offer new technologies, often of a startling level of advancement. Their requests usually involve the trade of living beings in odd numbers and varieties, such as one disabled Martian and three left handed kroleteans One of their current interests is in healthy meta-humans.No one knows what happens to the individuals concerned after the exchange
The Rachni resemble human-sized bipedal insects with a chitinous exoskeleton, four eyes, and a distinct, large, tapering head along with fully developed wings that allow them to fly over short distances. Each Collector appears to be little more than a drone with no distinctions between individuals. Although they do not appear to communicate vocally, since none are heard speaking, they have been heard to cry out in pain when shot or killed.
It has been speculated that the Collectors make these strange requests because of strange fetishes or gruesome culinary tastes. However, it is more likely that they perform genetic experiments on these subjects, possibly testing their viability for use in the creation of a Reaper. Regardless of the possible danger, their requests are often granted by fringe groups because the technology the Collectors offer in return is often extremely valuable, giving any race who receives it an immediate advantage before it becomes adapted to the galactic community.
In space, Collectors use the Rachi Cruiser for transportation of troops and abducted colonist.