[PhasmaFelis]

"Blind as a bat" is a common expression in English. Free Dictionary says it's been around since the 1500s, and theorizes that people thought their erratic flight was due to poor eyesight. https://idioms.thefreedictionary.com/blind+as+a+bat

[arthurcolle]

I was referring to the "poor as a church mouse" expression actually but thanks for the etymology regarding the other expression - sounds plausible.

[PhasmaFelis]

Ah, yeah. It's not so common these days. I associate it with the 19th/early 20th century, I guess? Not sure exactly, though.