AH, so THAT's why they get out of the rain.

My oldest-known version is a combo of yours, intersting, where the ants went down (WHERE? shouted by everyone else) into the ground (WHY?) to get out (OF WHAT?) the rain, boom, boon, boom. And you could also just sing Down, into the ground, boom, boom, boom. I think my family knew the simple one and then my older sisters heard the call/resopnse version at camp.