The Doxy is a small fairy-like creature that is covered with black hair. It is found in Northern Europe and America. Doxies are pests. They can infest houses, taking up residence in the draperies. Removing them requires a good supply of Doxycide.
They have sharp venomous teeth (FB). It's a good idea to have an antidote for Doxy venom on hand as well (OP6).
There was an infestation of doxies in Grimmauld Place's drawing room. Mrs. Weasley, Fred, George, Ginny, Hermione, Ron and Harry all spend a morning using doxycide to get paralyze them all. Fred and George sneak a couple of the immobilized doxies into their pockets so that they can experiment with the venom for the Skiving Snack boxes.