• Scientists found that 10 or more fire ants can stick together to build a life-saving raft in floods.
  • Fewer than 10 ants can’t form a stable raft because the “Cheerios effect” of fluid dynamics isn’t enough for so few struggling ants.
  • This effect can be used to engineer nanoparticles for biofluid emulsions, and the ant movements can inform the design of swarming microrobots.

How many ants does it take to build a raft?

This sounds like a riddle, and in a way, it is. Scientists whose interests in insects and fluid mechanics intersect have been wondering how fire ants stick together in water. When

In fact, fire ants don’t seek to clump together in water. Instead, they try to shove each other away. But research from the Georgia Institute of Technology in Atlanta, over the past few years may have an answer to the riddle. When 10 or more ants are close together in water, a property of surface tension called the “Cheerios effect” pushes them

This odd situation, described by the researchers in the fall 2021 issue of APS Division of Fluid Dynamics, doesn’t just apply to the fire ant species Solenopsis invicta from the wetlands of Brazil. If you’re a fan of Cheerios, you may notice that individual cereal pieces tend to stick together in the bowl of milk. Even other objects, such as paper clips, stick together, as long as they can float. Cheerios—and ants—are less dense than water, so they are buoyant.