Bat**** crazy

What is the etymology of the phrase "bat**** crazy" or "bat **** crazy"?

Does this have something to do with a malady afflicting guano miners?

Or is histoplasmosis or nitrate poisoning involved?

Bats = crazy. Probably from the way they fly around in a seemingly crazy manner. I don't know how bat-sh*t crazy would have evolved.

"Boring as bat sh*t" is a very common expression which has been around for at least 20 years in Australia, although why bs would be boring I don't know. Pamela