Territory

Species 8472 were first spotted in Borg space in 2373.  Conflict between Species 8472 and the Borg began immediately.  The Federation starship USS Voyager came across Species 8472 towards the end of 2373.  The information contained in this database has been downloaded from Voyager's computers.

Species 8472 are not from our universe.  They come from a place where they are alone, and nothing else lives there.  They travel to our universe through quantum singularities.  Species 8472 are interdimensional, and come from a place
where there are no stars or planets.  It is filled with an organic fluid, and not really space at all, but matter.  This space is referred to as fluidic space.

Ideology

They have a cold malevolence to them.  Their only desire is to conquer, and there is no negotiating with them.  Like the Borg ideology of assimilation and "resistance is futile",Species 8472's ideology is "The Weak Will Perish".
Species 8472 believe that we have contaminated their space by entering it, and believe that our galaxy is a threat to their genetic purity.  Thye want to purge our galaxy of our impurity.  Based on their experience with the USS Voyager and its alliance with the Borg collective, they believed that Starfleet was an invasion force, same as the Borg.

History

Species 8472 was encountered in 2373, when they were at war with the Borg. Further investigation revealed that the Borg started the war with Species 8472.  Species 8472 planned to invade the Federation by impersonating humans and other Federation races.  They have incredibly detailed information about Starfleet and human culture, leading to speculation that Species 8472 has already infiltrated the Federation.  However, some of their facts are inaccurate, which is the best way to figure out that they aren't who they appear to be.

Ships

Species 8472 use organic biomass ships (which appear to be actual living lifeform as opposed to just organic components as evidenced by the vertabrae seen upon entering the ship).  Each biomass ship has a crew complement of one. The ships seem to be impervious to Federation (or Borg, for that matter) technology:  ship sensors can't penetrate the surface of the biomass ship, transporters can't lock onto it, and the tractor beam has no affect on it.  It
has been demonstrated that the biomass can dissolve through the hulls of Borg ships and therefore can probably dissolve through the hull of the Voyager.  Wherever Species 8472 came from, their ships use warp propulsion with
anti-matter technology.  Inside the ship, there are organic conduits which carry an electro-dynamic fluid.  This quite possibly could be an energy source.  There is also a binary matrix laced with neural peptides, which could be their idea of a computer core.  The biomass ships have the ability to regenerate themselves.

Medical

Species 8472 is telepathic in nature, and at this point, it is unknown if they have a spoken language or not.  They emit a bio-electric field that disrupts the transporter, preventing getting a lock on or near them.  Narrowing the
transporter confinement beam doesn't work.  The bio-electric field also prevents tricorders from being able to localize the location of Species 8472.  The cells of this species are densely coded and have more than one hundred times the DNA a human cell would have.  They have an extrordinary immune response.  Anything
that enters the cell membrane are immediately destroyed.  Therefore, the Borg can't assimilate them.  They are highly resistant to all forms of technology.  However, species 8472 is vulnerable to the modified nanoprobes.  Species 8472 is made of the same material as their ships.  They are capable of living in the vaccuum of space with no life support.  They can also crawl along the hull of a starship without additional support.  They are also capable of regeneration. Species 8472 don't particularly like being in humanoid form and having to do things such as sleep, bi-pedal movement, and breathing oxygen.
 

Method of Attack

Species 8472 attacks with their claws whenever they can.  This will transfer their cells to the victim.  These cells, once in the victim's blood, will begin to consume the body from the inside out, essentially eating the victim alive. The victim will be conscious during this process because all sedatives and other treatments to the infection are neutralized immediately.  While the fire power of one ship is extrordinary, they can combine their fire power by forming a
circle with a number of other ships, with one ship in the center of the circle. All the ships fire at the main center ship, which collects the fire power and amplifies it out, causing enough fire power to destroy a planet.  Species 8472
are highly intelligent and devious.  When they enter the enemy's ship, it will do whatever is the most efficient way to destroy the ship.
 
 

Defensive Strategies

So far, the only theory as to how to stop Species 8472 is with modified Borg nano-probes which could attack the alien cells before the cells have a chance to destroy the nano-probes.