Observatory: Gracious Guests, Ants Pick Their Host Trees Out of a Crowd

Ants called Pseudomyrmex triplarinus live inside the leaves and trunk of Triplaris americana trees, where they take shelter and eat sugars, fats and proteins supplied by the tree. In return, they bite animals that try to eat the trees’ leaves, and they prune away plants that grow near them. Now researchers have figured out one way in which they can distinguish a foreign plant from their own.

A study showed that Pseudomyrmex triplarinus ants were able to recognize extract from different types of trees independent of the shape or texture of the material that carried it.

The scientists, working in Peru, found that the ants consistently pruned foreign seedlings that sprouted near their tree. They also removed 80 to 100 percent of foreign leaves experimentally pinned to the trunk, compared with only 10 to 30 percent of T. americana leaves.

Then the investigators treated identical strips of filter paper with leaf wax extracts from T. americana; with extracts from T. poeppigiana, a closely related species; or with plain solvents as a control. The ants attacked the control strips more often than the T. poeppigiana, and the T. poeppigiana more often than the T. americana strips. This suggests the ants could, to a significant degree, recognize the extract independent of the shape or texture of the material that carried it.

“These ants are very protective of their host tree,” said Jorge M. Vivanco , an author of the study and an associate professor of biology at Colorado State University. “It doesn’t matter if it’s a human, an animal, an insect or another plant species — they’re going to attack it. How they can differentiate the host tree from all other types of plants is the main contribution of this paper.”

The study was published Wednesday in the journal Biotropica.