Monday, May 9, 2011
Ants form raft to survive floods
The incredible floating fire ant
The Washington Post: When swept up by a flood, a colony of the critters -- thousands of them -- will save themselves by joining forces and forming a raft. They pile together and lock arms, legs and jaws. So bound, an ant raft can survive for months, sailing off to new lands.
Engineers studying animal oddities now report that together, the ants aren't just stronger. They're more buoyant. Airtight, even... 'Water does not penetrate the raft,' said Nathan Mlot, a mechanical engineer at Georgia Institute of Technology and lead author of the ant-raft report published in Proceedings of the National Academies. Even the bottom layer of ants stays dry... The uneven, hairy surface of the ant's skin explains this phenomenon. Bumpy, hirsute, or otherwise rough surfaces repel water... Duck feathers also repel water because of their tiny bumps...
Mlot and his colleagues gathered fire ants from the wilderness of Atlanta. Back in the lab, Mlot deposited colonies of 500 to 8,000 ants in large beakers. When gently swirled, each colony spontaneously formed a sphere. Mlot dropped these spheres into water... The ants on top of the ball crawled down to the water and grabbed onto other water-level compatriots. The next layer of top ants then crawled to the edge, and so on. In about a minute-and-a-half, each ant sphere flattened into a dome, then flattened further into a pancake shape -- a raft... This togetherness pushes each ant's individual air bubble against the next ant's bubble. The bubbles join, protecting the whole raft.
Image source here.