In their natural state, they resemble amorphous masses of seaweed-covered foam with long tendrils extending to all directions; and rhythmically pulsate creating a characteristic sound similar to a heartbeat. They feed on natural gas deposits and release a form of toxic gas. They are driven away (and can even be killed) by loud noises of some frequencies, and are vulnerable to high concentrations of oxygen. They are all linked by a hive mind, and will die immediately if the center of the colony is destroyed.
The Weed Creatures have barbs that can sting through Human skin and inject substances which make the subject dormant, and eventually turn it into a mindless host for the weed, which has complete control over the subject's mind. After injecting itself, the parasite not only takes control of the host but has access to any information from the host's brain. After some time, the host's body is taken over and starts to exhibit patches of weed growing from skin, increased vulnerability to oxygen and the ability to expel toxic gas from their mouths. This state can fortunately be reversed if the parasite is killed, even after the physical transformations have occurred.
- Doctor Who season 5 (Second Doctor) - Fury from the Deep (1968)