Study Of Fire Ant Rafts May Lead To New Developments In Self-Healing Building Materials [VIDEO]

By Ajit Jha on November 27, 2013 9:42 AM EST

Fire Ant Raft
In order to survive as a colony, fire ants form "rafts" to keep them afloat when heavy precipitation hits. (Photo: Nile Red, Flickr)

A new finding on the unusual physical nature of red imported fire ants truly could pave the way to new developments in robotics and engineering. It turns out that these creatures form "fire ant rafts," a kind of group assembly that behaves like a solid and a liquid, in order to keep their colonies alive through inclement weather. The discovery was presented to the American Physical Society Division of Fluid Dynamics in Pittsburgh on Nov. 26.

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Red imported fire ants, Solenopsis invicta, are among nature's most abhorred creatures - tiny little things with venomous stings. For example, the Queensland government in Australia considers them a serious social, environmental, and economic threat. In fact, they are named as a "notifiable pest" under Plant Protection Act, 1989, making it mandatory for the landlords to report their suspected sightings.

These fire ants originate from the Brazilian rainforests where heavy precipitation is known to cause flooding nearly twice every day. Fire ants must stick together as a colony to survive these deluges. So, the ants hook their legs and mouths together, as a survival strategy, creating a raft that make them appear as a living, breathing waterproof material. They can float for hours or even weeks in this form and wait for the floods to subside.

The ants are programmed to assemble rapidly in response to emergencies. Thousands of them collect together in less than two minutes, according to the Georgia Institute of Technology scientist David Hu. He has studied ant rafts for years and claims they are a living fabric. There are as many as 200 ants within a square inch of a fire ant raft. The size of a raft can vary. The largest ones are as large as a garbage bin lid. However, the average size of an ant raft is the size of a small plate.

Hu and his team are studying physical characteristics of ant rafts that they believe will prove valuable to material scientists who may be able to replicate their structures in robotics or other construction. Floating clusters as a feat of natural engineering could mean survival against floods and long distance migrations.

The study team used a rhemometer to study the physical characteristics of ant rafts that could contain living and dead fire ants. This instrument can measure the response of solid or liquid structures against applied force. The researchers found that external forces could be easily tolerated since fire ants within a raft constantly rearranged in response to external forces and bounce back elastically as the force is removed.

"No matter what you do, they are always constantly rearranging their bodies to respond to stresses," Hu said. "Where someone pushes on them, they initially act like a solid, but if you leave the plate, there they will also flow and respond. There are very few materials that act like that."

Their extremely flexible response made them able to effectively deal with any obstacle coming their way. The dead ants within the raft, however, behaved only like solids, according to Hu. So, they were discarded because they obstruct the integrity of the superstructure.

The study team hopes that their work will assist the creation of self-arranging robots ideal for tight spaces or self-healing building materials that can prevent further damage. The team is working to come up with a set of equations to describe the movement of these rafts.

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