Ants in your pants

Hi, my phrase of the day is "ants in one's pants." I know it means antsy or restless (my Mom said so), but where does the phrase come from? Thank you,
Sax
PS: we saw the entry re: fissle/fistle, but that didn't answer the question. Thanx...

If I find anything else, I'll post again. But the phrase is quite literal. If a person sits on the ground, like during a picnic, he or she probably will get ants in his/her pants. And that makes a person fidget.