This article is about the book. For information about the antthrush genus, see Formicarius (genus).
The Formicarius, written 1435-1437 by Johannes Nider during the Council of Basel and first printed in 1475, is the second book ever printed to discuss witchcraft. Nider dealt specifically with witchcraft in the fifth section of the book. Unlike his successors, he did not emphasize the idea of the Witches' Sabbath and was skeptical of the claim that witches could fly by night. The Formicarius is an important work for the study of the origins of the witch trials in Early Modern Europe, as it sheds light on their earliest phase during the first half of the 15th century.
Nider was one of the first to transform the idea of sorcery to its more modern perception of witchcraft. Prior to the fifteenth century, magic was thought to be performed by educated males who performed intricate rituals. In Nider's Formicarius, the witch is described as uneducated and more commonly female. The idea that any persons could perform acts of magic simply by devoting themselves to the devil scared people of this time and proved to be one of the many factors that led people to begin fearing magic. The idea that the magician was primarily female was also shocking to some. Nider explained that females were capable of such acts by pointing out what he considered their inferior physical, mental and moral capacity.
The work is further of note for its information regarding notably infamous figures of the time, one of whom was the sorcerer Scavius, who reputedly escaped his enemies on multiple occasions by metamorphosing into a mouse. Prior to his death Scavius was responsible for the tutelage of Stedelen in witchcraft.
The title is Latin for "the ant colony", an allusion to Proverbs 6:6. Nider used the ant colony as a metaphor for a harmonious society.