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Close to Home, Ants Get Angry

1 July 2004 (All day)
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Don't tread on me. Saharan desert ants will fight to protect their nest, even if the nest isn't there.

The Saharan desert ant (Cataglyphis fortis) takes no chances when it comes to homeland security. It viciously attacks ants from other colonies that get too close to its nest. Now researchers have found that the ant relies on the same internal navigation system it uses for foraging to decide whether an intruder has come too close for comfort.

Many animals fly into a defensive rage when they sense competitors edging in on their territory. But in the sandy Sahara, few environmental cues mark territorial boundaries. Behavioral neurobiologists Markus Knaden and Rüdiger Wehner of the University of Zürich in Switzerland wondered whether the sight or smell of the nest primes the ants for a fight or if their internal navigation system puts them on alert.

Previous research showed that the desert ants somehow keep track of every step and turn they take when out foraging for food and integrate that information to plot a straight line back home. The system apparently serves the ants well, enabling them to find their way in an environment devoid of landmarks and get back to the nest before shriveling up in the hot sun.

To test whether the ants' navigation system also plays a role in aggression, Knaden and Wehner placed a feeder 20 meters from a desert ant nest. Left undisturbed, the ants snatched a bite of food and ran straight back to their nest. But the researchers grabbed the ants as soon as the ants picked up a piece of food and moved them to a 40-meter-square grid 2 kilometers away. There, they turned the ants loose and let them run either 20 meters or only 5 meters before testing their willingness to fight other ants. The ants that ran the whole 20 meters--covering what would have been the distance back to their nest--were far more aggressive than the ones that only ran 5, the team reports in the 2 July issue of Science.

"This rules out that it's the presence of the nest that makes them aggressive," says behavioral neurobiologist Björn Brembs of the Free University Berlin. Rather, he says, when the ant runs a certain distance and direction, the brain switches gears from running home to fighting. Understanding what biological signals are involved in that switch is the next step, he says.

Related sites
Wehner and Knaden's Science paper
Wehner's site

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