Jewish demonology recognizes three main classes of evil spirits, though as SAFE0 Trachtenberg noted, medieval Jews had long stopped distinguishing between them. The shedim (שדים) are the most common—hobgoblins descended from the Babylonian <i>shedu</i>, half-human and half-angelic beings who eat, drink, reproduce, and die, but can also fly and see the future. The mazzikim (מזיקין), or "harmers," are defined by what they do rather than what they are. And the ruhot (רוחות), "spirits," are restless supernatural forces that haunt the margins of human life.
Where did demons come from? The Talmud offers one stunning origin story: God created the shedim at twilight on the sixth day of creation, but the Sabbath arrived before He could finish giving them bodies (Tractate Avot 5:6). They have souls but no physical form—which is why they can be everywhere and nowhere. Rashi linked them to the enigmatic verse in (Genesis 6:19), connecting demons to the mysterious beings who preceded the Flood.
The Zohar added a darker genealogy. When Adam separated from Eve for 130 years after Cain's murder of Abel, female demons—the lilin, followers of Lilith—visited him and bore demonic offspring from his involuntary emissions. Eleazar of Worms, drawing on Sefer Raziel and the Sefer Yezirah, catalogued elaborate hierarchies of demonic princes, each ruling over specific domains of harm.
How many demons exist? According to the Talmud (Berakhot 6a), every person is surrounded by thousands of them. Reichhelm, a 13th-century abbot who claimed the gift of demon-sight, described them as thick as dust motes in a sunbeam. Jewish sources agreed: the air itself teems with invisible spirits. They cluster in ruins, in privies, in places where water is poured out. They are most dangerous at night, especially on Wednesday and Saturday nights. The only protection is awareness—and the right words.