PAINFUL

Whistling Thorn Acacia

ACACIA DREPANOLOBIUM

One of the most wicked of the hundreds of acacias found throughout the world, this scrubby East African tree employs painful, three-inch thorns to keep browsers away from its lacy leaves. It is also host to a band of aggressive, stinging ants.

Four different species of ants have taken up residence in these trees, although they can’t occupy the same tree without going to war with each other. They live in the swollen bases of acacia thorns, which they enter by chewing a hole through the thorn. That small hole creates the strange whistling sound that the tree makes in the wind.

The ants are not only ferocious; they’re organized, too. Small militias patrol the branches looking for predators. They will swarm over a giraffe or other grazing animal to keep it from destroying their home. Other ants selectively prune the tree, allowing new growth only near their colonies so that they can enjoy the tree’s nectar. The ants will also chew climbing vines and other invasive plants down to stumps. If a tree occupied by a rival colony stretches its branches too close, the ants will decimate half of their own tree to keep the canopies from touching and creating a bridge to enemy territory.

And when the tribes do fight, they fight to the death. Researchers once tied the branches of neighboring trees together to provoke a conflict, and the ant corpses were piled a half-inch deep on the ground the next morning.

Meet the Relatives     Some species, including Acacia verticillata, secrete a chemical that induces necrophoresis, or corpse-carrying behavior, in ants. The little zombies carry the acacia seeds around as if they were their own dead, helping to disperse the seeds and start the next generation. Many also have thorns; the cat claw acacia, A. greggii, is sometimes called the wait-a-minute bush because its prickles will grab hold of a hiker and refuse to let go.