Not All the Bugs in Your Home Are Bad

This species of turtle ant, Cephalotes varians, harbors a diverse and co-evolved community of bacteria in their guts. Photograph by Gracen Brilmyer (FMNHINS62654).

When people find out that I am an evolutionary biologist working with ants (and the bacteria that live in their guts) they often ask me what we can learn from these ubiquitous insects (and their gut bacteria). The answer is quite a lot… from preventing rush-hour gridlock to avoiding taxiway problems at airports to designing the most highly effective wireless communications networks. These amazing social insects may also help us to better design the cities and structures of our built environment.  Ant homes (also called nests, mounds, colonies, hills, etc.) are similar in many ways to human homes. (In fact, check out a recent post by Clint Penick about the 10 ways in which they are similar. While humans are finally catching up to ants in the complexity of home construction, ants have already lived in complex, crowded cities and homes for millions of years.  By studying these societies, we can understand how they have overcome the obstacles of communal living on an evolutionary timescale.

Ants build and live in complex structures. Dr. Walter Tschinkel has perfected the art and science of casting the 3-D structures of ant nests. This species of harvester ant, Pogonomyrmex badius, digs species specific tunnels and chambers which increases in size and depth with the age of the colony. This nest was cast by pouring molten aluminum into the hole in the ground that the ants enter. As this species moves their nests each year, Dr. Tschinkel waited for the ants to move before pouring the molten metal. No ants were harmed in the making of this nest cast. Photograph by Charles F. Badland and courtesy of Walter R. Tschinkel.

As we begin to think more about the evolution of the indoor biome and how this may impact our health and well-being, I believe we can and will learn quite a lot from ants and other social organisms. We know that many aspects of our homes and cities affect our health including how clean we keep our floors and counters, how we dispose of our garbage and waste, where we bury our dead, and how air moves throughout our living spaces. Ants overcame these issues long ago (see Clint’s list to learn how ants use ventilation systems, control temperature in their nests, have garbage dumps, use anti-microbial cleaners, and more). All of these strategies are particularly important for keeping harmful microbes at bay and promoting the growth of the helpful ones. We have long appreciated that decreasing our risk of encountering harmful microbes prevents illness and increases our chance of survival (think of cooking food to decrease the chances of food poisoning from harmful bacteria), but the idea that microbes, bacteria, and germs can also be good for us has only recently begun gaining momentum.

Ants have overcome many of the obstacles we face when designing complex cities and living in cramped quarters, including the inherent risks of disease transmission. Borrowing the techniques that social insects employ may be beneficial, but this will require careful study of what works and what doesn’t. Unfortunately, it is not easy (or legal) to purposely manipulate human homes or cities to see what increases our risk of disease and death — but fortunately, ants are ideal models for these studies as they are easily and willingly manipulated. We can adjust airflow, change conditions known to promote or reduce bacterial growth, and introduce pathogens all within the controlled and replicable world of an ant colony. These kinds of studies would show what increases or decreases microbial virulence to determine which systems are most effective at keeping harmful microbes at an acceptable level. Perhaps more importantly, they can also show us how to promote the growth of the beneficial microbial community.

Many of our bacterial partners arrive from unexpected places. In some cases, we know they come from the people and pets we share our living spaces with (see this recent post by Rob Dunn on the microbes we share with our dogs and this article about the Hospital Microbiome Project). But there are lots of other ways that helpful and harmful microbes can get into our built environments including open windows, ventilation systems, and even the pests with which we begrudgingly share our living spaces. We have all seen the occasional ant on the kitchen counter, cockroach scurrying across the bathroom floor, spider spinning a web in the corner of the living room, and fly whizzing around the patio, but there are likely many, many more “guests” we share our homes with yet rarely see. To put this diversity in perspective, a recent project by the Your Wild Life team to document the “wildlife” we have living in our homes found over 70 families (this must include hundreds of species) of arthropods living in a single house. This begs the question, how many of the critters we share our living spaces with are responsible for moving helpful and harmful microbes around? No one has tackled this question yet, but I think we will learn a lot when we do. Are some insects better to have around than others? Should we promote the cohabitation of some “pests” in our homes, while working to exclude others?  Without sampling the microbes found on the insects and other animals we find moving between our rooms, homes, and buildings, we won’t know the answer to this. We have a lot to learn.

As someone that works on two groups of organisms that often get called “bugs”, I tend to gravitate towards the living things that make many people’s skin crawl. Ask any entomologist or microbiologist and they will tell you that both insects and microbes are essential for our own health and survival on the planet. This is why putting a diverse group of scientist, engineers, and architects together to discuss indoor evolution is exciting. I expect to see that what we learn about social insects (and ants, in particular) will translate into data on how to most effectively promote positive and healthy living spaces for humans. And maybe if we learn that the insects we share our living spaces are beneficial, I will stop being asked how to get rid of the ants on people’s kitchen counters.

Dr. Corrie Moreau is an Assistant Curator in the Integrative Research Center at the Field Museum of Natural History in Chicago, IL, USA.  Her research focuses on the evolution and diversification of ants and the many other insects, plants, and microbes they have mutualisms with. She tweets at @CorrieMoreau.