The Devil's gardener

Imagine this - you're forcing your way through the Amazon rainforest and you come upon what looks like an orchard - and there aren't any people around who could have made it:

According to local legend, peculiar clearings in the Amazon rainforest made up of a single tree species were created by an evil spirit. [...] "Someone walking around the jungle who steps into a devil's garden would immediately notice the difference between the garden and the surrounding vegetation," study author Megan Frederickson of Stanford University told LiveScience. "It looks a lot like an orchard – as if someone had come along and planted the trees."

Turns out the culprit is a species of ant. They use formic acid to exterminate the plant species around their nest that they can't utilize, leaving one species intact.