The incubus, also called “follet” in French, “alp” in German, “duende” in Spanish, and “folletto” in Italian, was an angel who fell because of lust for women according to many of the Church Fathers. This being appears to women often in the form of a sexual dream/nightmare, and in fact the Latin word for nightmare is “incubo”, meaning to lie upon. Its counterpart is the succubus, who appears to males. When a witch or sorcerer is associated with it, it is called a magistellus or familiar.
Succubus demons are the female counterpart to the incubus. They come to the beds of human men at night to seduce the men in their dreams. Many times succubi enjoy seducing monks. They have to draw the sexual energy from men in order to sustain themselves almost like a vampire needing human blood. In the past, they are generally depicted as quite frightening with wings and a snake-like tail. However, modern times have changed their appearance to look like a beautiful enchantress so that that can more easily seduce sleeping men to gain their energy.