In 2373, the Borg provoked a war with Species 8472 by invading fluidic space. Species 8472 defeated the Borg and launched their own counter-invasion of the Milky Way, sending hundreds of bio-ships through a string of quantum singularities in a region of space later nicknamed the "Northwest Passage".
Near the end of that year, the USS Voyager discovered a single regenerating bio-ship amongst the debris of 15 Borg cubes. The ship fired on Voyager, knocking it off-course before Voyager escaped. Many more bio-ships were detected as Voyager traveled deeper into Borg space. (VOY: "Scorpion")
After forging an alliance with the Borg, the Voyager crew developed nanoprobe-based bio-molecular warheads effective against Species 8472. Seven of Nine then took Voyager into fluidic space to force a confrontation; Voyager successfully destroyed four bio-ships within fluidic space, and thirteen more after it returned to normal space. Faced with this weapon, the remaining bio-ships retreated to fluidic space en masse. (VOY: "Scorpion, Part II")
A bio-ship was composed of genetically similar organic material to Species 8472 and thus shared their resistance to technology and weakness to modified nanoprobes. The ship was highly resistant to conventional weaponry and could regenerate itself if damaged. The hull was also impervious to sensors and tractor beams. It also had energy shields. Each bio-ship was piloted by a single individual.
Bio-ships were armed with a single forward-mounted directed energy weapon powerful enough to destroy Borg cubes with a few shots. Eight bio-ships, directing their firepower into an energy focusing ship, were capable of destroying a planet. Equipped with an antimatter-based warp propulsion system, the ship could operate both in its native medium of fluidic space and in the vacuum of normal space, and open quantum singularities to pass between the two. When in flight, the three fins on the bio-ship's rear section were extended.
Internally, the bio-ship had structures resembling flesh and bones. There was a network of organic conduits that carried electrodynamic fluid, possibly as an energy source, as well as a binary matrix laced with neuropeptides that may have functioned as a computer core. The bio-ship could dock to another vessel by "dissolving" through to its interior. (VOY: "Scorpion", "Scorpion, Part II")
When first encountered by USS Voyager in 2373, it was identified as a biomass, and was impervious to Federation technology. It did not register as a starship on sensors, however, it did register as organic bioreadings, but the sensors could not penetrate the hull. Furthermore, a transporter lock could not be established on the ship, nor did the tractor beam have an effect on it. It was first suggested by Chakotay of possibly being a space-dwelling organism or a biological weapon. (VOY: "Scorpion")
Ships of the class
The final draft of "Scorpion" gave the following description of this type of ship during the initial long-range viewing, "...a small, organic-looking BIO-MASS on the [Borg Cube's] hull. It's bulbous and ashen. Strange." As they magnified the screen, "We can now see what looks like the body of a "squid" attached to the hull...no tentacles...but it definitely looks like an organism of some kind."
The Species 8472 bio-ships were created as a CGI model built by Foundation Imaging's senior supervising visual effects animator, Adam "Mojo" Lebowitz. Their two forms of weaponry were devised by Visual Effects Supervisor Ronald B. Moore and Visual Effects Coordinator Cheryl Gluckstern. (Cinefantastique, Vol. 29, No. 6/7, p. 95)