Tea for Two Hundred (1948)

Donald is preparing a little picnic when he sees some ants passing by. He decides to tease one, ultimately by piling lots of food onto it. The ant eventually stumbles, but realizes Donald is sitting on a veritable gold mine. He rallies his fellow ants, and while Donald is napping, they cart him to a cliff and drop him into the river. When he returns to the raid in progress, he finds himself powerless to stop it. He dynamites the ant hill, but that only separates the ledge he's standing on, and he finds himself in the river again as the ants finish off a cupcake.