What metaphors are used in The Day of the Triffids by John Wyndham?

Chapter 2 is notable mostly for its narration of how triffids became an accepted, albeit mysterious, component of society. Here the author begins his exploration of the book's central metaphor, anchored in his repeated references to the triffids (and perhaps even the comet/satellite) as originating in Russia. In the context of these references, the triffids can be seen as a metaphor for the unknown, but vividly imagined, dangers of communism and socialism.