The Unseen World of Household Ecology: Living With Nature Indoors

Every homeowner knows the frustration of spotting an ant trail across the kitchen counter or finding a spider web in the corner of the living room. We clean, scrub, vacuum, and spray, determined to keep our living spaces free of unwanted visitors. But what if the very idea of a completely sterile home is an impossibility? Ecologist and author Rob Dunn, in conversation with This Old House host Kevin O’Connor on the Clearstory podcast, reveals a fascinating truth: our homes are bustling ecosystems teeming with life, both visible and microscopic. Rather than fighting a losing battle against nature, understanding the essential home preparation tasks for house guests of the microscopic and arthropod variety can transform how we think about domestic life.

The Hidden Biodiversity of the Average Home

When researchers began systematically cataloging the life forms living inside ordinary homes, the results surprised even seasoned biologists. The typical house contains hundreds of arthropod species, including insects, spiders, millipedes, and their relatives, along with thousands of microbial species. As explored in the Clearstory S2 Ep 3 podcast with Rob Dunn, the average home is far from the sterile environment we imagine it to be.

Arthropods: The Visible Residents

Dunn’s research, conducted through large-scale citizen science projects like the “Arthropods of Our Homes” study, surveyed more than 50 homes in the Raleigh-Durham area of North Carolina. The findings were remarkable:

• The average home contains between 32 and 211 arthropod species at any given time
• Common residents include carpet beetles, cobweb spiders, booklice, and gall midges
• Basements and ground-floor rooms host the greatest diversity of species
• Many of these creatures are not pests at all. They are harmless scavengers that have simply wandered indoors

Most homeowners would be shocked to learn that the spiders in their basements are actually beneficial. They prey on smaller insects that would otherwise become more numerous, providing a natural form of pest control that works around the clock without chemical intervention.

Microbial Life: The Invisible Majority

Beyond the visible arthropods lies an entire universe of microscopic life. Bacteria, fungi, and viruses coat every surface in the home. Dunn’s belly button biodiversity project famously demonstrated that even the humble navel hosts dozens of bacterial species, some found nowhere else on Earth. The same principle applies throughout the house:

• Kitchen cutting boards harbor bacterial communities distinct from those on bathroom surfaces
• Dust samples from different rooms contain unique fungal signatures
• Pet ownership dramatically alters the indoor microbiome
• The act of opening windows brings in outdoor microbes that mingle with indoor populations

This invisible ecosystem is not something to fear. Most indoor microbes are harmless or even beneficial, and exposure to a diverse microbial environment during childhood has been linked to lower rates of allergies and autoimmune conditions.

Water Cycles and Indoor Ecosystems

One of the most important factors shaping which creatures live in a home is moisture. Water availability drives the distribution of everything from mold spores to silverfish to cockroaches. Understanding the water recycling in the home lessons from the Clearstory revolution provides insight into how managing indoor moisture can influence the kinds of species that take up residence.

How Moisture Attracts Life

Different moisture levels create distinct microhabitats within a single home. A dry living room with forced-air heating supports different species than a damp basement or a steamy bathroom. Dunn’s research found that:

This table illustrates a critical point: the diversity of life in a home is not random. It follows predictable ecological patterns based on resource availability, just like any outdoor ecosystem. Homes with persistent moisture problems inevitably host more species, particularly those that thrive in damp conditions.

Managing Moisture Without Eliminating Life

The goal of home maintenance should not be to create a sterile environment. That is both impossible and undesirable. Instead, homeowners can manage moisture strategically to prevent the conditions that support genuinely problematic species while maintaining a healthy indoor ecosystem.

• Fix leaks promptly to prevent mold-friendly damp spots
• Use exhaust fans in bathrooms and kitchens to reduce humidity spikes
• Maintain proper grading and drainage around the foundation
• Avoid overwatering houseplants, which can create localized humidity
• Consider a dehumidifier in basements that consistently register above 60% humidity

Rethinking the Modern Home as a Habitat

The design of modern homes has inadvertently created ideal conditions for certain species while excluding others. Understanding this dynamic connects closely with the modern barnhouse vision for the 2021 This Old House Idea House, which explored how thoughtful design can balance human comfort with environmental awareness.

How Construction Choices Affect Indoor Ecology

Every building material, every design decision, and every furnishing choice influences what can live inside a home. Consider these factors:

1. Ventilation systems: Central HVAC systems distribute airborne particles, including microbes and arthropod fragments, throughout the entire house. Homes with well-maintained filters and regular duct cleaning have different microbial profiles than those without.
2. Building materials: Wood framing and cellulose insulation provide food sources for certain insects, while concrete and steel support different communities. The choice between hardwood and carpet flooring dramatically affects dust mite populations.
3. Sealing and insulation: Modern energy-efficient homes are tightly sealed, which reduces the exchange of indoor and outdoor air. While this saves energy, it also concentrates indoor pollutants and creates stable conditions that some species exploit.
4. Landscaping: Plants and trees close to the foundation create bridges for outdoor species to enter the home. Mulch beds against the foundation provide ideal habitat for millipedes, sowbugs, and other moisture-loving arthropods.

The lesson from Dunn’s research is clear: the supposed division between indoor and outdoor environments is an artificial one. Nature does not stop at the doorstep. Every home is connected to the surrounding landscape through air currents, water pipes, soil contact, and the daily movements of people and pets.

Species That Truly Belong Indoors

Some species have evolved specifically to live in human dwellings. They are synanthropic, which means they thrive in association with human buildings. The most famous examples include house sparrows, house mice, and German cockroaches, but the list is much longer. Dunn’s work has identified several arthropods that appear to be specialists of the indoor environment:

• House dust mites are microscopic arachnids that feed on shed human skin cells and thrive in bedding, upholstery, and carpets
• Booklice are tiny insects that feed on microscopic molds growing on paper, wallpaper paste, and stored food
• Carpet beetles have larvae that consume natural fibers, feathers, and dead insects trapped in floor crevices
• Brown-banded cockroaches prefer warm, dry indoor spaces rather than the damp environments favored by German cockroaches

These species have become so adapted to human homes that they would struggle to survive outdoors. Our houses are not just invaded by outside nature. They have created entirely new ecological niches that species have evolved to fill. As discussed in the Healthy Homes Clearstory S2 Ep 6, understanding this relationship is key to creating healthier living environments for both humans and their tiny cohabitants.

Practical Wisdom for Coexisting With Household Biodiversity

Once we accept that complete sterility is a myth, the question becomes how to manage indoor ecology wisely. The goal shifts from eradication to management: maintaining conditions that support human health while keeping genuinely problematic species in check.

When Intervention Is Warranted

Not every household guest is benign. Some species pose genuine risks to health and property, and knowing the difference between a harmless visitor and a genuine threat is essential:

• Termites and carpenter ants can cause structural damage and require professional intervention
• German cockroaches are associated with asthma triggers and can spread pathogens
• Bed bugs feed on human blood and can cause significant psychological distress
• Rodents chew through wiring, contaminate food, and carry diseases
• Mold growth in wall cavities can cause respiratory problems and structural rot

For these species, intervention is not just warranted but necessary. The key is to use targeted, least-toxic methods rather than broadcasting pesticides throughout the home.

Integrated Pest Management for the Home

Integrated pest management, or IPM, is a strategy that emphasizes prevention, monitoring, and targeted control rather than routine chemical application. Applying IPM principles to household ecology means:

1. Seal entry points. Caulk gaps around pipes, windows, and doors. Install door sweeps and weatherstripping. Repair damaged window screens.
2. Remove resources. Store food in sealed containers. Take out trash regularly. Fix leaky pipes that provide water sources. Declutter areas where debris accumulates.
3. Monitor populations. Use sticky traps in basements and crawl spaces to track what is present. Learn to identify common species rather than reacting to every sighting with alarm.
4. Use targeted treatments. When a genuine pest problem develops, use baits and traps rather than broadcast sprays. Spot-treat affected areas instead of fogging entire rooms.
5. Accept the background level. A few spiders in the corners and the occasional beetle wandering indoors is normal and healthy. These creatures are part of the home’s ecosystem, not signs of failure.

The Surprising Benefits of Indoor Biodiversity

Dunn’s research suggests that exposure to a diverse indoor microbial and arthropod community may actually benefit human health. The hygiene hypothesis proposes that reduced exposure to microorganisms in early childhood is linked to increased rates of allergies, asthma, and autoimmune diseases. A home that is too clean may paradoxically be less healthy than one with a moderate level of biological diversity.

• Children growing up on farms have lower rates of asthma and allergies, likely due to greater microbial exposure
• Homes with dogs have more diverse bacterial communities, and children in these homes have lower allergy rates
• Opening windows regularly introduces beneficial outdoor microbes that may help regulate immune function
• Garden soil brought indoors on shoes and clothing contributes to microbial diversity in house dust

This does not mean abandoning hygiene. Hand washing, food safety, and basic sanitation remain essential. But it does mean reconsidering the reflexive urge to sterilize every surface and exterminate every arthropod. A balanced approach to household ecology supports both human health and the natural world.

Conclusion: Embracing Our Perpetual House Guests

The conversation between Kevin O’Connor and Rob Dunn challenges us to see our homes through new eyes. We are not isolated from nature when we step through the front door. Instead, we share our living spaces with a complex community of organisms that have adapted to human dwellings over millennia. Far from being a sign of poor housekeeping, the presence of certain creatures indicates a functioning indoor ecosystem.

The practical takeaway is not to stop cleaning or to welcome termites with open arms. Rather, it is to become more thoughtful stewards of the indoor environment. Understanding what lives in our homes and why helps us make better decisions about construction, maintenance, and pest management. The window selection for the farmhouse in Fairfield County in the This Old House Idea House demonstrated how thoughtful design choices can improve ventilation and daylighting while maintaining energy efficiency, decisions that also affect the indoor ecosystem. Every choice, from the type of insulation in the walls to the frequency of vacuuming, shapes the invisible community we live among.

By learning to recognize the difference between a harmless house guest and a genuine pest, we can save money on unnecessary treatments, reduce our exposure to pesticides, and foster a healthier indoor environment for ourselves and the countless tiny creatures that share our homes. After all, as Rob Dunn’s work makes clear, we are never truly home alone.