In 2375, Voyager discovered Terrasphere 8 by chance after detecting an ersatz Federation signal.
Some Species 8472 were uncomfortable experiencing the lives of lifeforms so different from themselves, while others found elements of it enjoyable. Their goal was reconnaissance: to infiltrate Earth and gather intelligence on Starfleet's military capabilities and plans. In response, they built several terraspheres in the Delta Quadrant containing simulations of Starfleet Headquarters, and genetically modified themselves to resemble Alpha Quadrant species. Their conflict with Voyager led Species 8472 to dismiss the Borg as "irrelevant" and focus their efforts on Humanity, as they had proven themselves much more dangerous with the use of the bio-molecular warhead. Shortly afterward, as the Species 8472 grappled with a Hirogen hunter, Seven took the opportunity to beam them both to a nearby Hirogen ship. Captain Janeway intended to aid its effort, but Seven of Nine refused. This individual later boarded Voyager in an attempt to return home to fluidic space. One member of Species 8472 was left behind in normal space and was relentlessly tracked by a pair of Hirogen hunters for several months. ( VOY: " Hope and Fear")Ī member of Species 8472 struggles with a Hirogen hunter. The consequences of Janeway's actions with Species 8472 almost resulted in Janeway being assimilated by the Borg. ( VOY: " Scorpion", " Scorpion, Part II", " Prey").
Species 8472 withdrew to their realm, soon after, in fear of the new weapon. Armed with bio-molecular warheads which contained modified nanoprobes developed by The Doctor, Voyager destroyed a number of Species 8472 bio-ships in fluidic and normal space. Upon realizing this, Captain Kathryn Janeway decided to ally with the Borg to stop Species 8472, while also ensuring safe passage through Borg space. The Federation starship USS Voyager encountered Species 8472 around this time, during which a member of the species telepathically communicated their genocidal intentions to Kes. With their superior biological technology, Species 8472 drove the Borg back and launched a counter-invasion of the galaxy, annihilating large numbers of Borg drones, ships and even planets. However, Species 8472 proved immune to assimilation and the invasion of their realm provoked a war according to Seven of Nine, Species 8472 was the first species to offer "true resistance to the Borg" in their long history. The Borg encountered Species 8472 in 2373, after finding their way into fluidic space to search for more species worthy of assimilation.
History War with the Borg Main article: Borg-Species 8472 War