They are made of brown mud, and appear to be very roughly put together. Their hair is made of dried grass and they have gnarled and twisted roots instead of hands and feet. Their faces are large, lumpy and constantly change shape. Their teeth are gold, their red eyes shine like small electric lights, and they speak in gruff, hoarse voices. They wear stiff coats of dried mud, buttoned with lumps of coal. They are ruled by a King, whom they refer to as "your Mudjesty," and spend their time digging in mud, which they enjoy.
When the Scarecrow fell through the earth down the beanpole from which he used to hang, he was stopped by two Middlings, the King and his servant, Muddle, who demanded that he pay a toll. After he paid it with an emerald, they allowed him to continue his fall. (The Royal Book of Oz)