High speed video of the compressing fire ant cluster. We could see the ants continuously moving in the cluster.
Video of one layer of fire ants. We could see the fire ants acting continuously: bending their arms and bodies, detaching form and reattaching to each other, and moving around.
With ants continuously moving and acting inside, the fire ant cluster is able to resist outside forces and help them survive.
When fire ants are moving, they could dissipate energy of the outside forces like a liquid. On the other hand, they form some long ant links in every moment. These links allow them to hold together and restore energy like a solid. Therefore, the fire ants cushion outside forces.