What's the origin of "hung for a toad"? Where is it used?

The phrase I have heard most often from my father usually went like this:

Well I'll be hung for a toad!

Where did this saying come from and has anyone else heard it? My dad's dad & mother were respectively Scots & Irish if that helps. He would exclaim that saying when something was a surprise.

It's not mentioned in online dictionaries such as Merriam Webster.

Solution 1:

meta: Look up the word toad in a good dictionary, not the phrase.
*"Hung for a toad" is not a set phrase or idiom.

A toad is a [2 A] contemptible or detestable person (used as a general term of abuse)

"Well I'll be hung for a toad!"

should likely mean that one will get severely punished for behaving in a contemptible or detestable manner.