We have compared ourselves to ants, in our stories and fables, for thousands of years. As our cities grow larger and humanity becomes a predominantly urban species, we live more and more like ants do. The features of city life—dense urban environments, frequent physical contact, fixed homes used day after day—have countless advantages, but as we have witnessed with the Covid-19 pandemic, they make it much easier for disease to spread to all members of a society, whether anthropoid or arthropod.
Ants have lived in crowded colonies for millions of years. How do they prevent deadly microbes from blooming into pandemics?
To begin to answer this question, consider leafcutter ants, which eminent biologist E.O. Wilson called “the most complex social creatures other than humans.” They live in massive colonies with up to eight million members that can spread over thirty square feet and be twelve feet deep. The colony is a warm, humid, underground metropolis in which the atmospheric balance of oxygen to carbon dioxide is precisely controlled. Like us, the ants engineer their own climate, although unlike us, this engineering is not harmful to them or to the larger ecosystem. Leafcutter ants are fungus farmers, and these exacting conditions are essential for the growth of their crop—but they also create ideal grounds for invading microbes.
Ants do not have the option to socially distance, but over the course of evolution they have crafted their own solutions to some of the very problems we encounter today. Ant colonies are emergent systems whose challenges are addressed not by top down command and centralized control, but through a network of diverse inputs that connect and collaborate.
Good hygiene is essential for them, as it is for us. Just as we bathe and (with increased frequency) scrub our hands, ants wash their bodies and groom each other. They also clean the colony and take out the garbage. Waste removal is critical to the survival of any dense population center, be it city or colony. Leafcutter ants of the species Atta colombica dispose of their waste outside the nest. To ensure that garbage collectors returning from the dump do not infect the colony, a two-tiered labor system is used: refuse is first gathered and taken to a collection point, and then brought to the dump by ants that live outside.
With Atta cephalotes, a species I worked with in Costa Rica, the midden is located underground in special chambers. As ants weed and groom the gardens, removing parasites and spent fungus, they load the contaminated material into a special compartment in their mouth that contains an antibiotic. The waste is sterilized before it is even taken to the refuse chamber, echoing the way we now wipe down our groceries before bringing them into our homes.
Elsewhere in the nest, painstaking efforts are made to keep the chambers clean and productive. Leafcutter ants control the chemical properties of their subterranean world, carefully maintaining their gardens at an acidic pH of 5, which is ideal for their crop but detrimental to alien fungi. (When the ants are removed, the pH jumps to 7 or 8 and the garden is overrun by noxious microbial “weeds.”)
More impressively, leafcutter ants deploy antibiotic strategies to suppress the growth of harmful microorganisms. A specialized gland on the middle segment of their body secretes an antibiotic that is used to inoculate each piece of vegetation brought into the colony.
In addition, the ants harbor and maintain a bacterium that inhibits a virulent parasitic fungus that could otherwise spread rapidly and take over the colony. The smallest workers, who care for the brood and maintain the gardens, are covered in a white coat of this bacterium. To reduce the possibility of contamination to these vital areas of the colony, these tiny ants “shelter in place” and remain inside.
In another approach to keeping society healthy, wood ants (Formica paralugubris) exploit the protective properties of tree resin, a strong antimicrobial, to inhibit the spread of contagious disease. They distribute lumps of it over the surface of the colony and, like a doormat, the resin disinfects the ants as they walk over it. (The ants risk their lives to harvest the dried resin; in the process, many are stuck in sticky sap and become entombed in amber.) Wood ants also mix resin with formic acid secreted by their bodies to yield a potent antibiotic, making them the only animals other than humans that practice pharmacology.
Ants evolved over a hundred and twenty million years with natural selection refining what works and eliminating what did not. Colonies whose hygiene practices failed to prevent the spread of harmful microbes did not survive to leave descendants.
Coronaviruses have been responsible for at least three epidemics, yet we persist in creating conditions ideal for their spread. The mixing of wild and domestic animals, both dead and alive, in China’s “wet” animal markets is but one example. Another is our relentless destruction of the natural world, our incursions reaching deeper into untouched habitats and exposing us to novel zoonotic illnesses.
Our cities mirror ant colonies in many ways, but if we take a step back, it is possible to see our entire species, Homo sapiens, as one huge, interconnected colony, making a comparison with ants all the more relevant. COVID-19 has revealed, with shocking suddenness, that a pathogen that infects one group of people in one part of the world can swiftly affect us all.
Our response to the spread of COVID-19 has involved breathtakingly rapid adjustment of individual behavior at considerable personal cost, a worldwide collective action the likes of which few of us alive today have witnessed. It has served as a clear demonstration that we are aware of our interdependence, and that under threat, our species is capable of acting in unison, with shared purpose and common goals.
Will we be able to apply this mindset to address the vast and intractable problems of climate change? Like a pandemic, the climate crisis operates on a global level and an effective response will require collective action.
The ants’ ability to coordinate their behavior and act in concert is key to their enduring success. It helped them survive through the last mass extinction. What can we learn from them, and what choices will we make, as we confront this and other critical threats that loom on the horizon?