The story, The Destructors is actually an allegory for the decline of the post independent Sri Lankan state so the story is full of symbolism. The house actually allegorically represents or is the symbol for the Sri Lankan state. Greene uses personification to make the house a character in the story (for example upon Blackie's approach on destruction day, the house is said to look as if it had slept). In turn then the surrounding area represents or symbolizes the area around Sri Lanka, which was destroyed by blitzes (aerial bomb attacks). The misery and shadows symbolize the mood of the state and the people. War and political strife are dark times in states and countries and misery and shadows do well to represent those feelings. T. describing the boys as being worms symbolizes the destruction from the inside out. He doesn't want to damage the house, he wants to destroy it, to make it something other than a house because after-all destruction is really just creation in disguise, which was the point of bringing Sri Lanka down, from the inside out, to make it something entirely different than it was before.