Enemy is all around, and you’ll never see it

The American ecologist Rob Dunn and his colleagues have catalogued 200,000 species living in our homes.

Detail from the cover of Never Home Alone.

Hold the cornflakes. American ecologist Rob Dunn and his colleagues have catalogued 200,000 species living in our homes.

Three-quarters of those have been discovered in dust, bodies, water, food and guts. One-quarter are fungi. The rest are bugs, critters and plants. To read an entire book on these mind-bogglingly industrious and inventive microscopic populations is to change fundamentally how you feel about your home.

You will, for example, never sing in the shower again. You’ll be too busy worrying about the millions of amoebas, nematodes and the bacterial excrement washing down from your gunky shower head. You will try not to think about the many nibblers that have evolved specifically to be active while you sleep. You will want to have your dog put down.

In Never Home Alone, Dunn demonstrates, with enthusiasm bordering on malicious relish, how each part of our homes and each nook of our bodies is home to hairy-legged alien metropoles. What lives in your armpits or your nose or your fridge is ­entirely different to what lives in your mattress or your walls.

The first reaction to the news that we are not at all alone is to get out the bleach. For the past century, that is exactly what we’ve done.

But as Dunn points out, when you try to kill everything, the only things that survive are the fast-evolving, antibiotic-resistant bacteria. The super-critters.

“We now control much of the evolution occurring on Earth, albeit unwittingly and with sloppy orchestration,” he writes. “The use of novel chemicals as weapons favours the evolution of ever more behaviourally and chemically defended pathogens and pests, and leaves far behind the species that might benefit us.”

If killing everything is not the answer, what is? For Dunn, it is the “rewilding” of our homes. He points out that the Amish, who shun industrial farming and live closer to nature, have a lower incidence, for example, of asthma. Where you have biodiversity, you have better health. Where you are far removed from nature, eating processed food off bleached kitchen surfaces, you have Crohn’s disease, allergies, multiple sclerosis and other “modern” afflictions.

Dunn leaves his windows open and does more washing up by hand (to stop nasty dishwasher fungi spraying the kitchen). He decided against a dog — and the nematodes that come with it.

He uses soap and water, not antimicrobial soap, to wash his hands. He never kills spiders.

He points out that these solutions are nothing more than an educated guess. His, and our, knowledge of what each species does, how it interacts with us and what happens if we change its environment, is embryonic. We’ve only scratched the microbial surface.

He illustrates this with a jawdropping chapter on Toxoplasma gondii, a parasite with a fiendishly complicated sex life. It starts out in cat faeces waiting to be eaten by a mouse. From the mouse’s gut, it moves to its brain and then, through bacterial alchemy, makes it less risk averse. Why? To increase its chance of being eaten by a cat. Once the parasite makes it back, via the mouse, to the cat’s stomach, it can, finally, reproduce. “And they say online dating is tough,” jokes Dunn.

It has taken decades of out-there science to establish that we, too, could have our minds ­altered by Toxoplasma gondii, that those infected are less likely to make considered decisions, that they are more prone to schizophrenia.

Of those 200,000 species, there are many that could help us. It is no accident that some of the worst bacteria are found in the most sterilised places, hospitals, where they are ­constantly challenged by antibiotics.

“This quickly gets rid of any bacteria that aren’t antibiotic-resistant and rids the surviving bacteria of any competition.” As he puts it bluntly: “We’ve screwed up.”

The good news, he concludes, is that these super-strains struggle where there is biodiversity. If we can find a way to restore what we’ve killed, all may be well.

The bad news? There can’t be many people with Dunn’s almost obsessional level of excitement for dust, gunk and microbial poop. This is a good book about niche science, which ­deserves to be widely read.

Matt Rudd is a senior writer at The Sunday Times.

Never Home Alone: From Microbes to Millipedes, Camel Crickets and Honeybees, the Natural History of Where We Live

By Rob Dunn
Basic Books, 323pp, $39.99 (HB)