Answer: Herbicide

Deep within the Amazon rain forest, a region of Earth known for its intense biodiversity, you’ll sometimes stumble across large stands of trees that are, curiously, populated almost entirely by a single tree species, Duroia hirsuta. The stands look so out of place that the locals refer to them as “devil’s gardens” because of an old myth that the peculiar areas are the home of an evil forest demon named Chullachaki (and also known as Chuyachaqui).

Today, however, we know that the strange single-species stands aren’t the result of a demon setting up a home, but the result of a rather unique species of ants: Myrmelachista schumanni , or lemon ants—named such because the acids in their chemical defense system, released when the ants are crushed or attacked, give off a citrus smell.

The lemon ants build their colonies in Duroia hirsuta trees and cannot expand their colony without more trees. To facilitate growth of the colony, they systematically inject the leaves of surrounding trees and vegetation with formic acid, killing off any plants that compete with their host trees. While formic acid is a common toxin produced by a variety of ant species around the world, lemon ants are the only known species to have adapted the compound for use as an herbicide.

Although there is a limit to the size of a colony based on how effectively the ants can defend against intruders, devil’s gardens can grow quite expansive in size. The largest observed devil’s garden is over 1,300 square meters (roughly 14,000 square feet), encompasses 328 Duroia hirsuta trees, and is believed to be around 800 years old.