Ants can walk on the back wall now
The game is a side view, so a tunnel is really a slot cut into the dirt with more dirt behind it. For a long time the ants didn't know that. They could only stand on a cell that touched a wall, floor or ceiling, so in a wide chamber they would walk around the edge or let go and drop, and a shaft wider than 2 cells had a middle column nothing could use.
I noticed it while playing a young colony for about 20 minutes, a real ant can walk on dirt so there's no reason it can't walk on the dirt at the back of its own tunnel.

Now any open cell at or below the original ground line counts as footing. Above ground nothing changed (there's no wall behind open air), so they still need something to hold on the surface. They also stopped falling inside chambers, which I think was most of what made a busy nest look wrong.
It needed a second drawing of every ant, since one that is on the back wall is being looked at from the top. Workers, soldiers, the fire ants and both queens have one. The switch between the two poses as an ant steps off a wall still needs work.