"T'was twice the size of the biggest asteroid I ever did see, all stone and teeth and tentacles like some nightmare staring us right in the face. The cap't, he said it was just a moon at first and to think no more on it, but I's knew better. I told him I did, I says to him that there is no moon..."
- — Deckmaster Cybin Lyttle, Chartist vessel The Lone Pilgrim
The physiology and nature of the Void Kraken are largely unknown, even to the most well-travelled explorers of the Koronus Expanse. This is doubtless the result of their rarity and difficulty to hunt and detect, but could also be that they represent more than a single species of void behemoth, several variations on the beast mistakenly considered a single race of creatures.
Whatever the truth of the Void Kraken's origins, a number of facts are largely agreed upon by those who have come into contact with them. They are almost certainly some form of silicon-based creature, without blood, true bone, or fluid to keep them alive. Instead, it is believed by those few Imperial Adepts to consider the beasts that the Void Kraken draw their sustenance from the very space debris they often resemble.
Kraken appear to be solitary, asexual creatures that reproduce by dividing themselves, much in the same fashion as amoebas or single-celled organisms. A Kraken tears off a piece of itself and flings it at a world (ideally airless and devoid of life) to create a hatchling which then burrows into the surface of the planetoid, feeding off the rock for solar decades or even Terran centuries before emerging as a fledgling Kraken and flinging itself into space to hunt (another reason for choosing small asteroids or rocks with little gravity to overcome for the young).
There is speculation that Kraken might mate, and some process of fertilisation is required for these hatchlings, but so far there has been no proof, or conceivable way to tell a male Kraken from a female Kraken, if such things do indeed exist.
Void Kraken feed off minerals found in rock, which explains their interest in voidships. The hulls of most void-worthy vessels present a Kraken with a concentrated collection of metals, ores, and silicates for it to feed on, a tempting and tasty morsel for the beast. Small starships have the most to fear from the Kraken, as the beast's size and strength, especially when striking from ambush in an asteroid field or close to a world, can quickly overpower a ship and render it helpless to fight back.
Even larger vessels are not immune, however, and Void Kraken attack things many times their own size, latching onto them like a limpet mine. Only ship-borne weaponry is any defence against a Kraken, and only then if the vessel detects the Kraken early enough and manages to drive it off with broadsides or Lance strikes.
Once a Kraken has entangled a voidship, it only disengages when the ship has been consumed or (if the ship is much larger than the Kraken) once it has taken a substantial bite from its hull. This process of consumption is as ponderous as the Kraken itself, however, and it is possible for a particularly brave crew to venture out onto the hide of the beast while it is feeding and lay mines on it or try and cut away its tentacles.
Such a task is fraught with danger and the Kraken often reacts quickly to such "parasites" on its hide by throwing up small fanged tentacles to rake back and forth, scouring its stony flesh clean. Sometimes a Kraken declines to consume a voidship straight away, or, if it has fed enough on its hull, it may leave the wreck alone. In these cases, Kraken have been known to drag lifeless ships from one system to another, gathering the hulks around remote worlds or in deep space, possibly to feed on at a later time.
- Rogue Trader: The Koronus Bestiary (RPG), pp. 36-37