The Vervoids resemble human-sized humanoid plants with pink flower-like mouths that can open to release a cloud of poisonous gas, the smell of which resembles methane. Their bodies appear entirely covered in foliage and their hands are also flower-like and contain a central orifice from which deadly poison darts can be shot.
Vervoids are born from large pod-like structures, which open when exposed to light. Their lifespan is very short, spanning less than a year. Like most plants, their metabolism is based on photosynthesis. They are vulnerable to a rare Mogarian mineral called vionesium, which shares some properties with magnesium and when exposed to oxygen releases light and carbon dioxide in great quantities. The reaction is so powerful that it causes the Vervoid metabolism to be accelerated to the point where they shrivel and die within seconds.
They can also reproduce by fragmentation, with even a single fallen leaf on the floor being able to regenerate into an entire Vervoid. Similarly, Vervoid pollen entering an open wound can result in the Vervoid genes combining with the host organism, creating a disfigured mutant.
Shortly after their creation, the Vervoids were intended to be transported to Earth, aboard the spaceship Hyperion III, to be used as labor force, being deemed superior to robot workers due to their intelligence, versatility and fast reproduction. Unfortunately, the Vervoids felt threatened by their Human masters and attempted to take control of the ship and invade Earth, annihilating humanity and inheriting the planet for them. The Sixth Doctor discovered a way to destroy the Vervoids using vionesium, thus saving humanity.
Although originally presented to the court by the Doctor himself as part of his defense after being accused of irresponsible behavior, the Vervoid incident was notably used by the Valleyard to add an accusation of genocide against the Doctor, since he exterminated the entire species (even though they were an artificially created species consisting of a few individuals). The Doctor claimed that allowing the Vervoids to live would surely result in the extermination of the Human race. Eventually, the charges against him were dropped.
- Although there's no reason to suspect the Vervoids were not created to serve as labor force as their creators claimed; their abilities strongly imply that they were intended to be potentially used as bio-weapons as well. Specifically: that they can release poison gas from their mouths and shoot lethal darts from their hands, and possibly the ability to regenerate an entire individual from a single leaf. That is not mentioned in the serial, though, and therefore remains speculative.
- Doctor Who, Season 23 (Sixth Doctor) - Trial of a Time Lord episodes 9 - 12 (a.k.a. Terror of the Vervoids), (1986)