R-75 is the Stargate Command name for an insect created by the Priors of the Ori, possibly as a countermeasure to the vaccine for the Ori plague, to circumvent attempts to forestall their destructive nature. They prefer nighttime, but can function in the day, though they are usually lethargic without a food source. They are also sound sensitive, traveling by way of echolocation. As asexual creatures, they reproduce very quickly and live for a very short time, literally eating themselves to death.
Initially, they were herbivores, eating crops from the roots. When denied crops, their physiology adapts to become carnivorous, eating all of an animal life-form. The SGC had originally hoped to use R-75 as a countermeasure for the kassa crop, but the containment of the creatures failed when they were exposed to meat, killing everyone at the Gamma Site but SG-1 and the members of the International Oversight Advisory visiting the Gamma Site.
After the Odyssey rescued SG-1 and the IOA members, they released a toxin which killed the bugs. Soon after, two more planets reported the bugs, but Stargate Command presumably found an effective defense against them as they were never seen or mentioned again. (SG1: "The Scourge")