system
Given the following post, respond as if you're commenting on Reddit:
human
eli5, How do ant tunnels not collapse?

How do ant tunnels not collapse? Our mines always have supporting beams, but do ants so the same?
gpt
By being very very small and a bit sticky. 

There are two things in effect here. Firstly, small things are much more structurally sound than the same thing but bigger. This is because as you increase the apparent size, mass increases exponentially. Imagine a cube that's 2 meters on each edge. This cube's height, length and depth are all 2m. Its volume is 8m^3 (2x2x2), and its surface area is 24m^2 (2x2x6). Now imagine the same cube but 4 meters on each edge. It's volume is 64m^3 (4x4x4), and its surface area is 96m^2 (4x4x6). Its height (how big it looks) has been multiplied by 2, but its volume has been multiplied by 8 and its surface area by 4. A large tunnel has to support *far* more mass proportional to its size than a small tunnel does, so it's more likely to need supporting. 

The second thing is the material in question. Mines are carved into rock, and rock comes in layers. Typically, mines follow one of these layers, because they want to mine whatever's in that layer. The entire layer is made out of the thing they want to mine though, and if they mine the whole thing out, there'll be nothing to support the layer above. Mines must find compromises then - mine out as much of the layer as possible without causing the ceiling to collapse from too much weight being on too little support. Many mines fail to strike the right balance here, because rock layers contain faults and weaknesses that are difficult to predict, and get a partial collapse as the area between two supporting walls caves in. Additional supports can be added to allow more of the layer to be mined without the roof falling.

An ant is not trying to mine coal or iron, nor is it digging through heavy rock layers. Instead, it's burrowing through sand or dirt. This is much lighter, and so its much easier for the sides of the tunnel to support. It's also separated into many grains, so where in a mine an entire rock layer will collapse, in sand and dirt, most collapses are just a few little fragments falling off, instead of the entire thing coming down. Wetness of the particles makes them sticky too, and allows them to hold a shape better. This is particularly effective on the scale of ants because the stickiness force of water works better the smaller you get.