Summary:

The Eriarti are an extremely advanced race devoted to scientific research and the systematic enslavement and conquest of other species.

Evidence suggests that the Eriarti have been active on Earth since approximately 1000 AD, although the wreck of an Eriarti craft on Mars discovered in 2011 has been dated to 8000 BC. Many unexplained disappearances (Atlantis prior to 300 BC and the Anasazi in the 13th century AD) are now believed to be the work of the Eriarti.

In the Virgo's original timeline, the Eriarti brutally attacked the Federation planet Tanzara in 2267. In 2383, the Eriarti kidnapped several members of the USS Virgo for experimentation purposes. It was during this crisis that the Virgo crew obtained the Quantum Mirror technology. In 2384, the Virgo crew stopped an attempted biological attack by the Eriarti on Vulcan and the Romulan Empire, and saved the Alarans (a very primitive sentient species) from extinction at the hands of the Eriarti.

Excerpt from the USS Virgo database:

Homeworld: unknown
Government: unknown
Status: Hostile

Small, gray-skinned humanoids similar to those reported at UFO sightings on 20th century Earth. The Eriarti have, in fact, been interacting with Earth since at least the 19th-century and with other Federation races perhaps before then. They are extremely advanced and have the ability to manipulate the perception of time in other species and use their abilities to experiment on other races in preparation for conquering and/or eliminating them. They were responsible for a devastating attack on the Tanzaran homeworld in the 23rd-century which was defeated only by the intervention of the Federation and the Klingon Empire. The Eriarti, while very advanced, are cowards and will not attack opponents who may have a chance (no matter how slim) of defeating them.