Fire ants trap air between their bodies and interlink using mandibles and claws, forming a flat mass that floats. Brood and the queen ride on the upper surface. The raft is self-healing: ants that are pushed under climb back up, and the structure reforms around damage. Laboratory work at Georgia Tech showed the aggregation flows like a liquid under slow stress and springs back like a solid under fast stress.
This matters for invasion. Floodplain habitats in the native range select for the behaviour, and it lets colonies survive hurricanes and river floods that would drown other ants, then land and re-establish elsewhere.
The sting is often misdescribed. Fire ants bite first to anchor themselves with their mandibles, then pivot and sting, sometimes repeatedly in a circle. The venom is unusual among ants in being mostly alkaloids rather than protein, which is why the reaction is a white sterile pustule rather than a typical wheal, and why allergy to it behaves differently from bee and wasp sting allergy.