Ecology

Ecological catastrophes are unfortunate. But they can be utterly fascinating, too.

Witness the spread of so-called bark and ambrosia beetles, a collection of 7000 species whose expansion beyond their native ranges threatens trees around the world.

It's not the beetles' fault, of course. They've simply happened upon a brilliant life strategy: Rather than eating bark, which tends to be full of toxins produced by trees to discourage predation, they eat fungus that eats bark. It's one of the animal kingdom's greatest and most unappreciated symbioses.

"You know how famous leafcutter ants are because they grow fungus? Those groups evolved this just once. In the bark beetles, there are at least 11 independent emergences," said biologist Jiri Hulcr of North Carolina State University. "Go into the rain forest in South America, and you see the power and diversity of these fungus farmers. You'll barely see a tree without sawdust falling off. That's the fungus farmers at work, drilling through the trees and planting their fungus gardens."

Every group of bark and ambrosia beetles has its own unique collection of fungi, carried in specialized pockets on their bodies, in their armpits and on their backs and in their mouths, always ready to be seeded. "Chop a beetle's head off, grind it up, spread it on agar and you will see the most marvelous organisms growing from it," Hulcr said. "Those are the fungal symbionts. And they are virtually unknown."