A journey to California, Costa Rica, and beyond in a celebration of the remarkable, efficient leafcutter ant…
by: Marie Gethins
At least once a year during my California childhood our home had an ant invasion. Tiny, brownish-black Argentine ants streamed across the windowsills after heavy rain. They frightened and fascinated me, marching single-file back and forth, six legs scuttling, antenna waving. Their visits ended when my father set out small green bottles of bait.
These industrious creatures often have starring roles in horror films. Late-night cable television fodder of my youth, I have a mental collage of screaming humans fleeing the awkward march of elephant-sized ants. Them!, It Happened at Lakewood Manor, Phase IV, Legion of Fire: Killer Ants. The IMDb database lists fifteen of these classics. Perhaps The Hive has the best tag line: “Death Is Their Picnic!” In an interview on the Irish Late Late Show, Joan Collins recounted that her lead character’s battles in Empire of the Ants left her scratched and bruised. Inevitably, humans are no match for these highly organized, often radioactively enhanced, menaces.
In Costa Rica’s Manuel Antonio National Park, a line of leafcutter ants crossed my path. During this first encounter, I was transfixed. A steady parade of small jade flags danced before me. They carried improbable loads many times larger than their size. I read leafcutters harvest more foliage than any other group in the neotropics. Cattle rancher turned conservationist Jack Ewing noted that they harvest more than fifteen percent of all rain forest green matter with a single colony of seven or eight million utilizing as much as a cow. Four days later in Sarapiquí, I took another solo walk. I followed a narrow trail amidst dense plant growth and stepped over busy leafcutter queues every few meters. At the start I noticed a fallen green banana leaf as long as my forearm. When I returned a couple hours later, it was skeletonized. I nudged it with my boot toe. No sign of any remaining stragglers. As jungle debris cleaners, leafcutter ants play an important role in the Costa Rican eco-system.
I asked a local guide about these efficient harvesters. He led me into the fiery afternoon sun and we followed a line of leafcutters to a mound of reddish soil. He said finding their homes was easy in this reforested compound, but the ants can travel up to a kilometer to find foliage in human-populated areas. The colonies are highly specialized with four castes of worker ants that wildly range in size. These castes are further divided by multiple roles. At the top of their society, the queen can be more than three centimeters long and live for twenty years. Leafcutter colonies can be up to six meters in depth, have 1000 to 1500 connected chambers of varying sizes, depending upon purpose. “The design drains away rain, controls different humidity and temperatures for the eggs and fungus,” he said.
A discussion on Reddit postulates that the Pyramids of Giza were inspired by ant colonies like leafcutters. The online posters do not give ants enough credit. My stooped and crawling journey to the King’s Chamber in the Great Pyramid was along a single, claustrophobic tunnel with seemingly no air flow. The overall design includes just three chambers. Oldest of the Seven Wonders of the Ancient World, it also is the only wonder that remains almost intact. However, leafcutter nests are architecturally far more complex and have much better ventilation systems. These too are impressive achievements.
The local guide told me leafcutters are very clean. As larger ants collect fodder and carry it back to the nest, smaller ants ride on top of the leaf cleaning it in prep for fungi installation. These tiny workers riding shotgun also protect the harvester ant from parasitic fly attacks. At the colony complex all refuse (dead compatriots, unused foliage, ant waste) is piled into the bottom which decomposes to produce heat rising through the chambers. This efficient biomass conversion may have renewable energy implications with the U.S. Department of Energy building a leafcutter lab. My guide’s gestures became increasingly animated as he provided details.
Leafcutters are more than hunter/gatherers. “Very sophisticated farmers,” my guide said. While they eat some of the greenery they collect, most of it feeds a fungus that serves as their primary food source, almost resembling bread. It’s a symbiotic relationship. The ants can’t survive without this exact fungus and the fungus depends upon the ants‘ cultivation skills. When a young queen leaves to form her own colony, she takes some of the fungus with her. I am dubious. Such specificity. How did that happen?
A group of Smithsonian scientists have traced the genomic evolution of leafcutters. Their ancestors survived when an asteroid wiped out most of the dinosaurs some sixty-six million years ago. Fire and ash cloaked the Earth. The ants’ secret? Adapting to living in darkness and eating fungus. Scientists theorize that over many generations, not only did the leafcutter ancestors make major lifestyle changes, but elements of their biology also altered. Over time, they lost the ability to produce an amino acid, becoming totally reliant on the fungus as their sole food source.
I thought of potato blight and the resulting nineteenth-century Irish Famine. In five years, Ireland’s population fell by a quarter through death and emigration due to dependence upon a single crop. Nothing has ever attacked the ants’ fungus? Turns out the leafcutters have this sussed too. Some have bacteria on the underbelly of their exoskeleton, while those that are in constant contact with the fungus are almost entirely covered by it, appearing dusty white. This bacterium, pseudonocardia, acts like an antibiotic to fight invasive molds and undesirable fungi without these invaders becoming resistant over time. There are several theories as to how the leafcutters manage this feat, but no one is certain.
My jungle stay concluded, I arrived at a gated community in Atenas for my artist’s residency. Cattle munched grass balancing on steep hillsides that surrounded the large houses. Morning mist rose off mountains in feathery strands. I took a walk through the neighborhood of sharp descents and heart-pounding climbs. Gardens had an array of colorful blooms: magenta, red, orange, yellow, purple. Butterflies in matching tones fluttered between bushes heavy with flowers. Palms bordered driveways, waving in afternoon breezes. I paused to enjoy a moment of tranquility. Movement on the road edge caught my attention. A flow of leafcutter ants marched towards a russet dirt pile. A specimen plant landscape, each home had carefully clipped lawns and hedges. Other than palms, I didn’t recognize plant life familiar from the past two weeks. Yet, the leafcutters toiled with similar green flags.
Back at the residency, I mentioned my discovery. The director frowned. She and the house manager had just dealt with a leafcutter invasion. While I assumed leafcutters restricted themselves to native plants, turns out they are opportunists and have a foliage testing protocol. When a scout discovers a new plant, she cuts a sample, leaving a trail of pheromones for collectors to follow if it proves suitable. At the nest, she presents the potential material to a tester ant who places a sample of fungus onto the leaf to see if it will grow. If successful, the workers scramble into action and homeowners may find their expensive feature plant swiftly stripped.
Early in the morning, the house manager and I searched for ants along the driveway. We looked under leaves, diligently searched palm tree trunks. He explained that the previous afternoon he had painted a white pesticide, designed specifically for leafcutters, onto their backs. We found piles of curled, large soldier corpses; their super motorway deserted. He speculated any painted ants that made it back to the nest might be groomed by other members, distributing the killer formula. “Very effective. The only one that works on leafcutters,” he said. Later, when I saw a photograph of a bacteria-covered worker, I thought he could be right.
However, the battle extends beyond gardens. Their deep colony networks can undermine structures, causing subsidence. At pre-Colombian Guayabo National Monument, near the Turrialba volcano, leafcutter nests caused ancient buildings and paths to sink. The streams of leafcutters and their reddish dirt piles along modern roads are likely to cause the same destruction. This clash between human domestication and Nature is an old one. As a child I enjoyed my brief observations of Argentine ant invasions, but I was relieved when they no longer paced our window sills. One expat Atenas resident told me she likes to help leafcutter stragglers that fall out of line. She picks up ant and foliage and returns them to the march assembly. Her neighbors preferred extermination. With approximately twenty-eight percent of Costa Rica designated as protected lands, the industrious leafcutters appear to have ample space to gather foliage, build complex colonies and farm specialized fungi. I leaned back in a poolside lounge chair to enjoy my host’s decorative garden saved from the latest leafcutter invasion.
The research and writing of The Ants Go Marching was facilitated by an Irish Arts Council Agility Award.
Marie Gethins’ work appeared in many nice places and has been selected for BIFFY50, Best Microfictions, and Best Small Fictions. She is the flash fiction editor for Banshee, a co-editor of Splonk and lives in Cork, Ireland, but does a fair amount of marauding.
