It's an interesting idea, and I love the sorts of structures you can build.
What I find really odd is the concept that the ants will only target the oldest block you selected, and that the ants can't really walk through each other. Because what happens is that once you have more than 30 or so ants, they start piling up, and adding more ants doesn't really get much faster.
I've found the most efficient way to use the ants is to ignore the normal anthill shapes and just expand the cavern out wider and wider in a big square, so there's as much room as possible for the ants to walk past each other. But even then, there are times where the ants just stay in once place, waiting for the ants in front of them to finish collecting their blocks before stepping in. And ants still have to go back to the top of the map to deposit what they picked up, which always causes pileups.
Unfortunately, the game isn't as much of an RTS as it could be because there's no way to assign separate groups of ants to different tasks, and it's not as much of an idle clicker game as it could be because of all the waiting around that the ants do.
Maybe there could be a feature where ants go to the nearest selected block instead of the oldest selected block?
I love the sound design!