Creatures of the night

If someone says, “You’ve got bats in your belfry,” they’re saying you’re insane but harmless.” Variations of this insult include, “to be batty,” or “to go batty.”
This expression arose because the flying mammals known as bats often roost in bell towers. Should the bells ring while bats are there, they fly wildly out and behave in a seemingly crazy manner. The earliest mention of “bats in the belfry” is 1911.
We have several other bat expressions, for example, “as blind as a bat.” This simile, first recorded in the 16th century, replaced an older one equating blindness with beetles and moles. In fact, bats, beetles and moles have something in common — they’re largely nocturnal.
However, bats are not blind, although they navigate via sonar and have the ability to make sudden 90-degree turns, which appear to happen when they sense, rather than see, some obstacle in their flight path.
If Simon arrives “like a bat out of Hell,” he’s moving very rapidly. Many sources attribute this saying to First World War British Royal Flying Corps slang. But Charles Earle Funk claims it was used in the U.S. at least as early as 1900 (2107 Curious Word Origins, Sayings & Expressions).
“Bat out of Hell” probably arose because bats dislike low places and light. Traditionally, Hell is located beneath the earth and is a place of constant fire. It would be the last place any self-respecting bat would wish to find himself and it’s easy to imagine the haste with which he’d flee if he did end up in Hell.
Early 15th-century slang adopted the word bat for “prostitute,” probably because prostitutes, just like bats, emerge when it gets dark.
“Old bat,” referring to a nagging or disagreeable woman, evolved from this use of bat for prostitute.
In poetry, bats are associated with nightfall and darkness. Here’s Francis Bacon, writing in 1620: “Suspicions amongst thoughts are like bats among birds, they ever fly by twilight.”
Years ago, when bats got into our lake cottage, I didn’t even know bats are mammals, which is a misconception shared by many. In fact, the OED says these animals were once officially classified as birds. They’re mentioned in the Bible as “fowl.”
Many believe bats to be rodents, but rodents belong to an entirely different biological order — rodentia. Bats are of the mammalian order of cheiroptera.
Our ancestors called the bat, flittermouse, a word directly related to the German word for bat — die Fledermaus — and to the Dutch, vleermuis.
Still older than flittermouse is the Middle English back, a word now found only in some dialects. Scottish English retains a remnant of back in its word for bat — bawkie bird. Back apparently originated in the Norse bakka, and is still heard in the term aften-bakka (evening bat).
Bat, in the sense of “club” or “stick,” is unrelated to the word under discussion and is of Celtic origin. Similarly, batman and other such military jargon are related to neither the club nor the animal. The military word originates in French.
Meanwhile, don’t invite a bat into your house. It might be Dracula.