Floating Ant Rafts and Swarm Robotics

Red imported fire ants (Solenopsis invicta) have a unique ability to cling together and form a floating raft whenever their underground tunnels flood. This raft can hold together and carry the colony for weeks or until the water recedes. These ants have a hydrophobic cuticle, and the cuticular texture creates an air bubble. These tightly knit bodies create a buoyant, water-resistant foundation for a floating raft. While other species of ant can float on top of water due to their hydrophobic cuticle, Solenopsis invicta is one of few species to exhibit rafting behavior. This behavior is one of many that aid in its successful dispersal.

Ant rafts have a constantly changing shape, and are made up of structural and surface ants. Structural ants are those that pack close together to keep the colony afloat, while surface ants march freely on top of the raft. The queens and eggs are safely tucked in the middle. The everchanging raft shape is caused by a behavior called “treadmilling”, where structural ants circulate to the surface of the raft, while free-walking surface ants burrow into the lower structural levels. Together, this cycle contracts or expands the raft, allowing for the construction of a narrow bridge that branches away from the body of the raft. These extensions are built to help raft riders “feel around” their environment and reach out for land or another such surface where the colony can safely disperse.

There is still a lot left to learn about ant rafting. One study created a series of models in which simulated ant individuals had to follow a simple set of instructions to carry out successful rafting behavior. Researchers hope that understanding rafting behavior and creating successful models will provide inspiration in the design of autonomous active systems such as swarm robotics.


Read the research: Wagner et al, 2021, Wagner and Vernerey, 2022

From TexasInvasives.org