When the USS Voyager made contact with them, Species 8472 were engaged in a war with one of Star Trek's perennial antagonists, the Borg.
[1] They made peace with the Federation by negotiations with Captain Kathryn Janeway of the Starfleet vessel USS Voyager in the later 24th century.
A member of Species 8472 is left in the Delta Quadrant during the retreat and is relentlessly hunted by a group of Hirogen for several months.
Concerned about the threat posed by humanity, Species 8472 builds 13 "terraspheres" in the Delta Quadrant and recreates Starfleet Academy within, as a staging ground for an intelligence gathering mission on Earth.
[2] The Guardian's Vera Rule said that their design reminded them "of HR Gigerish bio-nastiness but with Ray Harryhausen animation".