Imaging being dumped into the water far from shore with dozens of your companions. Can your group survive? It is no problem if you are a fire ant.
The red imported fire ant is a pest in southern North America, but is native to the rain forests of South America. In its native habitat, floods are common and fire ants can find themselves adrift. When dropped in water, fire ants will use their legs and mouthparts to grasp onto nearby objects. Some of those objects may be other ants. This behavior causes the ants in water to link together and form a raft.
Each ant is somewhat water repellent and able to trap air bubbles. A raft of ants will trap air under the ‘raft’ and enable the entire mass to stay afloat. While a single ant may struggle to remain afloat, a group of ants in a raft can float effortlessly.
Nathan Mlot and fellow engineers recently completed a study that is published in the April 25, 2011 issue of PNAS. They are among the many engineers that are studying insects for ideas that can be applied to robots. If your robot lands, in the water, floating would be useful.
Kryptonite for ant rafts: Soap. The ant raft requires surface tension of the water for support. If soap is added to the water, the cuticles of the ants wet, and they can no longer trap air between their bodies and the water. This causes the raft to sink and the ants to drown.
Overlooking its diminutive size and shortcomings in soapy solutions, the ant raft has attractive traits with respect to man- made flotation devices. It simultaneously provides cohesion, buoyancy, and water repellency to its passengers. It can be con- structed quickly (in approximately 100 s) without any additional equipment. It can accommodate thousands to millions of passen- gers with zero casualties. But perhaps most strikingly, the ant raft is self-assembling.
Many of these benefits are due to the ant’s small size. At the scale of millimeters, ants have great strength, high speed, and the ability to trap air pockets when submerged, which in turn makes their rafts water repellent. These abilities will likely vanish at large sizes. Roboticists interested in building biomimetic ant rafts will need to design robots that can both reversibly attach to and traverse over one another. Moreover, they will need to under- stand which processes of raft assembly process are coordinated (such as ant-to-ant gripping) as opposed to stochastic (ant trajec- tories).
The entire article complete with video clips of ants forming rafts is worth the read.