Most of the monsters in this list have been technological or animal in nature, with the possible exception of the Blob, which holds the crown of most terrifying Jello-based lifeform in the galaxy. But the Triffids are even more terrifying, being plant based. These leafy life forms differ from their brethren in their apparent intelligence and the way that they are able to walk. They first terrorised humanity in a novel by John Wyndham before appearing in the popular 1963 movie, a 1981 mini-series and, latterly, a second BBC mini-series which sees Eddie Izzard confront the fearsome foliage. Why are they so terrifying? Silently, unexpectedly, they take over much of mainland Europe following a meteor strike that blinded half the population. They're intelligent, and their poison is deadly to humans. The very ideas of plants reclaiming the land from the cities is a striking and terrifying one. Whether you think they're monsters or simply reclaiming the planet we spoiled, theres no denying that these shambling, venomous plants are responsible for the near downfall of civilisation as we know it!
