I don’t know about you, but I am batty most of the time.
Bats in the belfry
Bats are, of course, the erratically flying mammals and ‘belfries’ are bell towers, sometimes found at the top of churches. ‘Bats in the belfry’ refers to someone who acts as though he has bats careering around his topmost part, i.e. his head.
It has the sound of a phrase from Olde Englande and it certainly has the imagery to fit into any number of Gothic novels based in English parsonages or turreted castles. In fact, it comes from the USA and is not especially old. All the early citations are from American authors and date from the start of the 20th century; for example, this piece from the Ohio newspaper The Newark Daily Advocate, October 1900:
To his hundreds of friends and acquaintances in Newark, these purile [sic] and senseless attacks on Hon. John W. Cassingham are akin to the vaporings of the fellow with a large flock of bats in his belfry.”
Ambrose Bierce, also American, used the term in a piece for Cosmopolitan Magazine, in July 1907, describing it as a new curiosity:
“He was especially charmed with the phrase ‘bats in the belfry’, and would indubitably substitute it for ‘possessed of a devil’, the Scriptural diagnosis of insanity.”
The use of ‘bats’ and ‘batty’ to denote odd behaviour originated around the same time as ‘bats in the belfry’ and the terms are clearly related. Again, the first authors to use the words are American:
1903 A. L. Kleberg – Slang Fables from Afar: “She … acted so queer … that he decided she was Batty.”
1919 Fannie Hurst – Humoresque: “‘Are you bats?’ she said.”
“Bat” is used to describe many things not related to hanging upside down:
blind as a bat
completely blind. (Bats are not really blind. *Also: as ~.) He lost his sight in an accident and is as blind as a bat.
not bat an eyelid and not bat an eye