You're making a good argument, but it's still flawed.

The entire concept of the "soul" determines that any living creature in possession of one is capable of more than just instinctive patern and reproduction. Ever seen a bear paint a portrait? Ever heard of a wolf not killing an elk because he knew it was wrong? The reason you haven't seen those things is because animals don't have souls. Simply being capable of building an anthill isn't grounds for being considered a soul-bearing creature. Rivers are capable of carving canyons, does that mean the Snake River has a soul?