Weed creatures were living algae grown to mammoth proportions that could hiss and squeal. They had no shape or form, with no head, eyes, mouth, or any features of known marine life; only tendrils and tentacles. The creatures made up a colony which possessed a nerve centre, with smaller colonies of seaweed clumps as an advance guard for the creatures. (PROSE: Fury from the Deep)
The weed fed on natural gas and generated massive amounts of foam. The weed reproduced rapidly, generating a pulsing sound like a heartbeat. They could sting and infected any human who touched them, allowing the weed to mentally control them, also gaining intelligence from the human brain. Both the weed and infected humans could produce poisonous gas. When the Second Doctor tried to convince John Robson that the weed controlled his mind, he responded "the mind does not exist. It is tired. It is dead. It is obsolete. Only our new masters can offer us life. [...] The body does not exist. Soon we shall all be one." The creatures were vulnerable to oxygen and high-pitched sounds, forcing infected humans to whisper so as not to damage the weed. If the weed infection was killed, the humans would be returned to normal unharmed. (TV: Fury from the Deep)
The weed was an "alien life-force from the dark depths of the ocean." (PROSE: Fury from the Deep) The Seventh Doctor once described the weed creatures as "primeval", existing since the days of the dinosaurs in Loch Ness. (PROSE: Christmas on a Rational Planet) Ancient mariners supplied a drawing of the creature in the middle of the 18th century, which appeared in a book of legends and superstitions the Doctor owned. (TV: Fury from the Deep)
In the late 20th century, a weed creature was sucked up by an off-shore Euro Sea Gas rig in the North Sea, where it came in contact with maintenance workers and infected them, including Oak and Quill, two engineers at the refinery commanded by Robson, who was later infected himself. The creatures used them to commit various acts of sabotage around the refinery, and in the space of a few days, the weed took over the crews of the off-shore rigs as the base of its nerve centre. Additionally, the weed accidentally infected Maggie Harris instead of Frank Harris, and Van Lutyens when the creatures attacked him. The possessed Robson told the Doctor that "our new masters" needed him to help with "the conquest of the human planet." Realizing that sound affected it, the Doctor used a recording of Victoria Waterfield's screams to destroy the creatures and their nerve centre, releasing the infected humans. (TV: Fury from the Deep)
Behind the Scenes Edit
It is always assumed, but never explicitly stated, that the weed creature is native to Earth. However, the weed makes reference to conquering "the human planet," and the novelisation repeatedly describes the weed as "alien."