Where does the expression “poor as a church mouse” come from and What does it mean?

The expression “poor as a church mouse” means: Mighty poor; about as deprived of the necessities of life as the “fly on the wall” of which mothers used to recite lugubriously to the children:

Poor little fly on the wall,
Ain’t got no shimmy-shirt,
Ain’t got no pettiskirt,
Ain’t got no nothing at all!
Poor little fly on the wall.

But our church mouse is not found only in English-speaking countries.

The Germans have the same saying, arm wie eine Kirchenmaus; in French it’s gueux comme un rat d’eglise, and it is found also in other languages.

The English saying goes back to the seventeenth century, but was probably taken over from French.

It is likely that it arose from some folk tale relating the sad experience of a mouse trying to find food for itself and its starving little ones in a church.

No pantry, no meal bag, no grain bin made the struggle for existence most difficult.