Like psychic spiders, dromes spin dreams out of people's images (and those of other creatures). The dreams are traps, but though there are signs, you may not realise you have passed into such a dream. The drome likes watching dreams, and if you eat anything in the dream, you will want to stay there for ever. It will watch you eating dream food until you starve to death, then it will eat you. They appear in the dream, and can be killed there with imaginary weapons. This is, in most cases, the only way of escape. Outside the dream they are large and pale and puffy, and can be beheaded in the ordinary way.
Dromes appear in Fairyland in The Wee Free Men. Fairyland is not their natural habitat. They are there because they have been kidnapped from some other universe by the Queen, for whom illusion is the natural coin of existence. She uses them like sheep dogs to herd dreams (and Tiffany Aching), and keeps some like guard dogs in collar and chain.
When Tiffany is taking her brother and Roland out of Fairyland, she wants to enter the world depicted on the packet of Jolly Sailor pipe tobacco, associated with her grandmother, Granny Aching. She relies on the ability of a small drome to create the world for her. Tiffany was able to exert some management in this dream, and get it to run more according to her rules. The drome appeared in the dream, paying no attention to them. Tiffany told the Feegles not to harm it. It seems that dromes know about the sea, and this one was home-sick for it. It was sitting by the sea-shore, and probably thought it was at home. The Queen had said of them contemptuously, they're not much more than a walking sponge. It appears that their natural prey may be crabs.