Shove Voles (and any other digging creatures) cannot dig straight down in solid terrain. Here's an example of this. The vole is in the center tile, with Show Navigation on. Tested on version Breath of Fresh Air 471883, with no mods.
To be more particular, they can't transition from one solid tile to another if they're moving straight down. Things to note:
- They can exit the bottom of a tile to be walking on the ceiling. You can see this on the left side.
- They can also dig from the top of a tile down into the tile. (Not shown.)
- To reach the stone in the bottom leg, the vole must wander all the way around on the outside.
- The vole can travel down the right leg, but only by zigzagging down. (It *does* have diagonal down transitions.)
- The vole can dig up the top leg, however, it is unable to dig back down! When it reaches the top most stone tile, it is permanently stuck! (I've tested it. You could probably build a vole snare this way. )
- Build a "vole snare": an upside down U-shape, three tiles wide, made out of steel, and at least three tiles high.
- Fill the interior with vole-diggable stone.
- Wait for a vole to enter. (Or teleport it over there with debug tools.)
- The vole can't leave.