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tissues unpalatable or even deadly, in much the way our bodies fight a viral infection by producing antibodies.61 Plants damaged by leafcutters don’t escalate their defenses in this way, an unexplained oversight that allows colonies to harvest from the same tree again and again over the years.62 But despite the inadequacies of plant deterrents, the ants seldom completely denude full-sized native trees. Some researchers have suggested that leafcutters are “prudent pruners,” taking only a portion of each plant so it can recover for future exploitation.63 Still, it’s doubtful that ants are more sensible than humans when it comes to resources. They likely extract foliage as fast as they can, at times removing enough leaves—20 percent or more—to adversely affect a tree’s survival and reproduction.64 Yet they depart after taking the best leaves. In fact, like a kid who’s eaten enough chocolate to make herself sick, the ants can tire of certain plants, shunning a once-choice species for weeks.65 Foliage-cutting workers particularly avoid a plant species when their small comrades on the gardens detect signs of fungal ill health, suggesting that the fungus may be informing the ants of its needs.66

Foliage isn’t the only thing leafcutters take from trees. Fruit, seeds, and flowers make up the bulk of their collections during tropical dry seasons, when fresh leaves are scarce.67 Rich in calories and containing few noxious chemicals, these plant parts, which workers remove directly from plants or snatch after they fall in near-mint condition, can be more sought after than foliage. The ants also collect the pulp of fruit discarded by birds or mammals and extract seeds from animal droppings, adding any attached pulp to the fungus gardens after discarding the seeds in their garbage heaps.68

With their sweet tooth for fruit and sap, it’s a surprise that Atta workers have never been seen drinking from the sugary nectaries on plants that other ants visit so readily.69 Nectaries encourage predatory ants to protect foliage and flower rather than cutting them up, as leafcutters do; but how do the same nectaries keep leafcutters away? Perhaps their fluids contain fungicides that discourage leafcutters. No one has investigated this possibility.

Leafcutters are concerned with more than hunting down plant parts—they must guard against becoming prey themselves. Once in the early 1990s, I squatted for three days straight in the narrow space between strangler fig roots near one of the Mayan ruins at Copán where priests had once performed ritual beheadings. I was looking for a phorid fly, and I knew I had found one when a leafcutter worker threw herself back to make a quick jab at a tiny speck that appeared suddenly over her head. A phorid floats around leafcutter trails like a dust mote until it swoops down on a worker’s head, inserting an egg through the ant’s neck or mouth. Some flies even find the carried leaf fragment a convenient site to cling to while they insert an egg.70 The hatched maggot then consumes brain and muscle until finally the ant’s head falls off—hence one common name for the phorid: the decapitating fly. The worker I watched warded off her pursuer, but if she had been carrying a leaf—making her unable to move fast or defend herself—she would have been an ideal target.71

Because decapitating flies need to see the ants in order to aim for their heads, some leafcutters forage only at night, and only the workers too small to be parasitized venture out during the day. This strategy compromises productivity, however, because the smaller ants are less effective at cutting and carrying most kinds of foliage than the bigger ants that emerge after dark.72

It appears that the best strategy for dealing with these pests, like most leafcutter strategies, involves a specialized labor force. As workers cut foliage, they stridulate, producing a vibration that travels through the ant’s body to her mandibles. This causes the leaf to stiffen, but unlike with an electric carving knife, this doesn’t improve the speed and efficiency of the cut;