I'm beginning to think that elephants are pretty wimpy creatures, especially for ones their size. First came the Mythbusters (video below), who demonstrated that elephants might really be afraid of little white mice. And now there's a study in Current Biology showing that ants deter elephants from munching on acacia trees.

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Biologists Jacob Goheen, of the University of Wyoming, and Todd Palmer, of the University of Florida, noticed that African elephants avoided eating Acacia drepanolobium trees—which host to a variety of symbiotic ant species—but not other types of acacia. When the scientists removed the ants from the A. drepanolobium trees, the elephants chowed down. But when the trees harbored ants, Palmer says, "the elephants avoided those trees like a kid avoids broccoli."

The ants are effective guardians for the acacia trees because underneath their tough hides, elephants are pretty sensitive: the insides of an elephant's trunk has a lot of nerve endings. (Giraffes, though, aren't deterred by the ants. They just flick the insects away with their tongues.)

These insect defenders might be having an even larger effect on the African savanna ecosystem, the scientists say. When there are enough elephants around, they can destroy so many trees that they convert wooded areas into open grassland. The ants may be preventing that. "It really is a David-and-Goliath type of story," says Palmer. "These little ants are up against these huge herbivores, protecting trees and having a major impact on the properties of the ecosystems in which they live."