National Geographic : 2000 May
n Costa Rica a Pseudomyrmex ant rips apart a vine that grips leaves of an acacia tree (right) where the ant's colony resides. If left to grow, vines could weigh down, shade, and possibly kill the tree. In West Africa a Crematogasterant smashes butterfly eggs on a Barterialeaf (below). Hatching caterpillars would eat the leaves of this tree, the ant's home. In both cases, specialized ants-often of species living nowhere else-tend trees day and night with the diligence of obsessive gardeners. Ants and plants have developed many curious relationships, some positive, some negative. Extreme exam ples occur with tropical plants called myrmecophytes, or "ant plants," which provide their insect guests with hous ing and often food. Many of these ant plants are vines or other types of tree top vegetation, but in the examples shown here, the hosts are the trees and shrubs themselves. I have explored, doc umented, and marveled at whole groves of ant trees in Brazil and Borneo, in areas where biting and stinging ants are the true lords of the jungle. Often the ants' behaviors can be interpreted as self-serving: The worker killing eggs gets a meal; the one gnawing vines destroys a route that might be used by invading enemies. In other cases workers defend particular parts of the plant that affect their tree's long-term health and reproductive ability with no apparent immediate benefits to the ants. Either way the interaction tends to be beneficial in the long term to both ant and plant-a symbiotic relationship that ecologists call mutu alism. But as I will show you, sometimes this relationship breaks down, as when parasitic ants seize control of a tree. Ecologist MARK MOFFETT contributed the two earlier installments of this "Ants and Plants" series: "A Profitable Partnership" (February 1999), an overview of these curious relationships, and "Friends and Foes" (May 1999), which focused on other species of ant plants.