Muggles' Guide to Harry Potter/Magic/Doxy

Overview
A Doxy (otherwise known as Biting Fairy) is a small fairy-like creature, covered in hair with two pairs of arms and two pairs of legs. Doxies have two rows of sharp, venomous teeth.

Extended Description
Doxies are pests; Doxycide, a black liquid that effectively knocks them out, is needed to dispose of them.

Doxies are encountered in Harry Potter and the Order of the Phoenix when an infestation of them was found in the curtains of the drawing room at number twelve, Grimmauld Place. Fred and George, who had been hired to help with the spraying, secretly pocketed a large number of Doxy eggs, which were presumably used when developing Skiving Snackboxes for Weasleys' Wizard Wheezes.

In the run-up to the O.W.L. exams in that same book, one of the students, named Howard Dingle but otherwise unseen, claims to have powdered Dragon claw available for sale. Hermione, who is a Prefect, confiscates and examines it, and finds it to be dried Doxy droppings.

From a throw-away comment by Aberforth Dumbledore in Harry Potter and the Deathly Hallows, "They'd be on you like Bowtruckles on Doxy eggs," we surmise that Doxy eggs are a favoured food for Bowtruckles, when they can find them. Doxy eggs are apparently hard to find.

Analysis
Doxies are not described in the books; though Harry sees them quite close to and actually has to spray one of them that is headed for his face, the author does not go into detail as to what he sees. This description is courtesy Magical Beasts and Where to Find Them, by "Newt Scamander".