Intellectually I knew that Dorymyrmex bureni could dig nests 1 to 2 meters deep into the earth. A long slender vertical tunnel. (This would be like you going out in your yard and digging a tunnel just big enough for your body... a mile deep. And doing it so expertly there are no cave ins)
But seeing them really do it? Being able to watch the progress as they go deeper?
Watching them find the sand tube, get excited and start digging. The way the number of ants on the project swelled when it became clear that there was someplace deeper to dig to! Makes me a little emotional. They are so small but so ambitious.
It made me sad when I saw them trying to make tunnels in the shallow sand I provided in their outworld. That's what inspired the sand tube. I could see they wanted, needed to dig!
I would be cute if this were the case, but I think it's just much more efficient and easier to make a structurally sound tunnel when one side is a solid object.