A bedbug pictured in an image from a scanning electron microscope.Credit: Eye of Science/SPL

Never Home Alone: From Microbes to Millipedes, Camel Crickets, and Honeybees, the Natural History of Where We Live Rob Dunn Basic (2018)

Rob Dunn invites us on a safari in pursuit of the wildlife teeming on our bodies and in every corner of our homes. For him, the creatures that sprawl in the human navel and under the bathroom shower head elicit the kind of wonder most of us would feel only on seeing the denizens of Tanzania’s Ngorongoro Crater or the Great Barrier Reef off Australia. Dunn is more than an informed and entertaining commentator, a David Attenborough of domestic biodiversity. He is a scientist whose research group at North Carolina State University in Raleigh made many of the discoveries described in his fascinating and illuminating book, Never Home Alone.

Dunn and his colleagues have used the concepts and techniques of community ecology to tease apart the functioning of a mostly ignored ecosystem: the human home. Their research enriches our understanding of ecosystem function, and — more grippingly — gives us insight into how our interactions with living things in the domestic habitat affect our health and well-being. The book is structured around sub-habitats in our homes — our bodies, rooms, water supply, pets and food. It considers an awesome range of organisms, from the rich fungal flora on bakers’ hands to the diversity of fly larvae in our drains.

We discover that warm, moist shower heads are ideal for the growth of biofilms containing trillions of bacteria, including Mycobacterium species that are harmful to human health. Dunn and his colleagues invited thousands of volunteers globally to send in samples from their bathrooms. The researchers are finding, for instance, that the more a water supply is treated with chemicals designed to kill microbes, the greater the abundance of pathogenic strains of mycobacteria. We also learn that the numbers of plant and butterfly species in our gardens are correlated with the robustness of the community of microbes on our skin; that some German cockroaches have evolved to perceive glucose as bitter, thus avoiding poisoned bait; and that dogs can give us both heartworm and a top-up of beneficial bacteria from their microbiomes.

The message of Never Home Alone is clear. The health of an ecosystem depends on its biodiversity: this is as true of our homes as of a mangrove swamp. Two factors, notes Dunn, are important. Simply by chance, a home containing more species is more likely to include organisms (especially microbes) that are vital in sparking our immune systems into life. And an ecosystem with niches fully occupied by diverse species is likely to be resilient and resistant to invasion by pests and pathogens.

We rightly fear the handful of domestic species that can harm us, such as lice and Legionella bacteria. But all-out chemical warfare is not a viable defence. It scythes down thousands of other species, and the target rapidly evolves resistance and flourishes on the blank slate we have thoughtlessly provided. This story is familiar from the overuse of antibiotics and pesticides, but Dunn’s book is the first to apply it across the range of domestic wildlife, from bacteria to bedbugs.

Dunn is a man on a mission. He is determined to recruit others to his research programme, to hunt for camel crickets in basements and to send samples of armpit flora, face mites or sourdough starters. He champions citizen science — as long as the citizens have curiosity and focus. The book opens and closes with a supreme exemplar of a lay scientist: seventeenth-century Dutch businessman Antonie van Leeuwenhoek, who pioneered microscopy and discovered bacteria and protozoa, opening up the universe of microbiology. His discoveries — based on everyday substances in his Delft home, such as saliva — and the wonder they excited in him epitomize the ideas in Never Home Alone.

Just one of Dunn’s arguments fails to convince. He asserts that some organisms, such as fruit flies and house mice, are important because they have become iconic model lab species, or because, like the Penicillium fungus, they could be sources of drugs. He suggests that by understanding the biology of, for example, domestic camel crickets — which thrive on very poor diets — we might learn new ways of breaking down intractable materials such as plastic. Quite so; but none of it depends on the fact that these organisms can be found in homes. Biologists find useful animals anywhere, from the axolotl to the hagfish and the Xenopus frog.

The results of the projects described are important. The indoor biome is huge. Humans are an urbanizing species, and in most cities, the combined floor space of homes and apartments exceeds that of the ground space outside. If we are to chart a harmonious settlement with the species living with us, we need to understand as much as possible about them.

I think this research has even broader significance. Since the Darwinian revolution, we have accepted that, biologically, we are one species among millions, subject to the same laws of evolution by natural selection. It is less clear that we have accepted that we are also subject to the same ecological laws. We know we can control, disrupt and destroy the ecosystems of the world, but we tend to imagine that we do so from inside a hermetically sealed personal bubble. By reframing our homes and selves as ecosystems, we are forced to contemplate how we fit in with the complex community of organisms with whom we share our lives.

The book has one final message. We have “farsighted” ecologists (Dunn’s term), whose eyes are fixed on the distant, charismatic ecosystems of rainforest and coral reef. We also need near-sighted ones who will study the half-hidden communities closely quartered with us in our homes. This book is their battle cry.