The gist of it is that 30% of studied ants do 70% of the work in digging tunnels. Other ants come in, see that it is too crowded, and don't try to force their way in in an effort to prove they're working hard to the other ants. This ends up being an ideal strategy for the colony because overcrowding reduces the overall work throughput, but requires all ants to be comfortable allowing some of their ant peers to work less while remaining in the vicinity of where work is being accomplished.
Pretty interesting stuff, if you ask me! :)