Never Home Alone – your household biodiversity

[A message from David Duthie, the former public information officer for the Ramsar Convention (wetlands conservation) — if he says this is a worthwhile book — it is.



Parties to the Convention on Biological Diversity all commit, in Article 6a, to developing a “strategy and action plan” for their national biodiversity and also, in Article 6b, to mainstreaming that strategy and action plan into other landscape or economic sectors.

“Never Home Alone”, authored by Rob Dunn and recently released by Basic Books, and reviewed (twice) below, demonstrates that within our own homes – homes, not even gardens! – we could have literally hundreds of “housemates” for which you could develop a household strategy and action plan that goes beyond a “scorched earth” chemical attack.

My copy of the book is still in the post, but the two reviews below give a good flavour of the book and the real enthusiasm with which Rob has developed his “niche”, looking at the biodiversity in and immediately around us.

I found the thought experiment of making my house more biodiversity-friendly using some of the normal “ingredients” of a national biodiversity strategy and action plan (PAs, invasive policy, waste management, etc.) quite interesting and I think that Rob would probably give my house a pretty good score as it is – and brought back memories of the cane toad living behind the toilet of our shack when I was a conservation volunteer in Costa Rica (where cane toad is native) a long time ago!

Best wishes

David Duthie

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Moths, maggots and microbes: our 5,000 creepy-crawlie housemates – and the man who loves to hunt them

Biologist Rob Dunn is the David Attenborough of the domestic sphere, uncovering everything from microbes in the shower to spiders in the basement. He goes on safari in the dusty corners of one Copenhagen home

Lars Eriksen

Thu 28 Feb 2019

The good news is that I will never be home alone again. The bad news – well, it’s not in fact bad news, but it is slightly unsettling – is that I share my home with at least 5,000 other species: wasps, flies, spiders, silverfish and an exotic bunch of wild bacteria.

All that information is apparently contained in a patch of grey dust I have just swabbed with my right index finger from a door frame in my living room. It’s like a DNA test of my house, says Rob Dunn, a 43-year-old American biologist who has come to my house in Copenhagen to hunt microbial life. He carries no lab gear and his blue crewneck jumper and striped Oxford shirt are hardly the combat suit of an exterminator. But with every discovery we make, with every spider we find lurking in the corner or each swab of dust, he displays an almost childlike sense of excitement. He swears and smiles, even whoops with delight: “This dust sample contains bacteria, your body microbes, your wife’s body microbes, your child’s body microbes. If you smoke weed we would find marijuana DNA in there. Everything is visible, but it’s also present in every breath. Every time you inhale, you inhale that story of your home.”

Dunn is to house insects and indoor bacteria what Marie Kondo is to neatly folded shirts. He wants us to study the wildlife in our homes and realise that what we discover should spark much more joy than fear. When he began working as a biologist he went to the jungle to study wild beasts, but now his research is dedicated to species much closer to home: to the flies, spiders and bacteria hidden in every nook and cranny of our kitchens, bathrooms and basements. To the “jungle of everyday life”, as he describes it in his new book.

Never Home Alone tracks how we have been disconnected from the ecosystems of our homes. It’s a book of hard truths – I now know that I shed 50m flakes of skin every day, providing food for thousands of bacteria, and that cockroaches are basically our perfect interspecies Tinder-match. It also confronts our irrational relationship with cleanliness. Our modern instinct might be to swat a spider on the kitchen worktop or blitz creepy crawlies into oblivion with antimicrobial sprays, but we could be killing useful allies, according to Dunn: “The key thing is that your life is going to be full of life. And your only choice is which life. Our default is that we try to kill everything and fill our houses with stuff that’s totally terrible for us. We might kill 99%, but that leaves 1% – and that 1% is never the good stuff.”

Dunn is in Copenhagen for work and has agreed to come to my home to go through dusty corners and spider webs to point out where I might find some of the 5,000 species I bunk with. I suspect our 110-year-old house, shared with another family, is a fertile hunting ground, and Dunn seems optimistic. Using a screwdriver and tweezers, he pokes at light fittings and sifts through the basement, which can be a mould-friendly hangout during sticky, wet summers.

While I’m making coffee, Dunn lets out a yelp: “Oh yes, this is good!” He has spotted a globe-shaped lamp hanging in the basement hallway, and in the bottom of the hazy glass cover is a Pollockesque pattern of dead wildlife. He tips the contents of the lamp on to a fold-out table and uses the tweezers to organise the harvest: two types of fly, a wasp, a meal moth, some aphids and various planthoppers. He takes a closer look at two of the dead flies: “I can tell they are likely to be the same species, but I don’t know for sure until I look at their genitals.”

He turns to the silver-shiny meal moth. “Isn’t it just beautiful? It moved in with humans in ancient Egypt and has moved with humans again and again.”But how would it have ended up in our home?“

This meal moth could have come in with grains.”

Like from a box of cereal?


Dunn wants us to see our homes the way we see our gardens. There are pests and pathogens we need to control – those that make us sick – but we also want to preserve diversity. He says fewer than 100 species of bacteria, protists and viruses cause nearly all infectious diseases today. We try to keep these in check with vaccinations and antibiotics, and by washing our hands. But that leaves us with a jungle of tens of thousands of other species, many of which we know little about, but which Dunn’s work suggests can often be more beneficial than harmful. For example, studies have shown that a higher diversity of bacteria on people’s skin – bacteria linked to soil and plants – can reduce the risk of allergies. He also mentions the discovery of a bug that could be a new source of useful enzymes:by testing the microbes in the gut of the camel cricket, found in many American homes, Dunn’s research team discovered bacteria that were able to break down industrial waste and turn it into energy. Making “cool discoveries” like this and enlisting the public to sieve through their homes for wildlife has spurred interest in a field he says has been neglected for too long.

“The first drawings of microscopic life are all of household species,” says Dunn, “but once we figured out the germ theory of disease it shifted, and both scientists and the public started to think that what was indoors belonged to pest control. Ecologists went to the Galapagos, we went to the rainforest, but it pushed us away from the home and it left us with this huge blind spot.”

Dunn grew up in rural Michigan, hunting snakes and turtles, building tree forts and being “more curious about nature than your average child”. Today, he is a professor in the department of biological sciences at North Carolina State University, where he has spent the past decade involving his colleagues and the public in studying the microbial landscape of our bodies and our homes. Part of the thrill of his new book is the sense of discovery and engagement with the world outside the lab. We head deeper into the basement, to the water-heating system, where one of the pipes has a leak; water drips into a chalk-crusted yellow bowl. Dunn grabs the bowl and tips it on to its side so we can see the puddle: “You could start a sourdough loaf with this.” The water heater is an example, he says, of the extreme conditions we create in our houses. These specific ones are similar to what you might find in an Icelandic geyser, which means that our basement heating system now attracts bacteria that would normally thrive in volcanic hot springs. He moves on to a sprawling mess on the wall next to the boiler. “That’s a lovely spider web,” he says excitedly. I feel a strange sense of pride and relief that my lack of cleaning is potentially boosting the ecosystem I inhabit. “This kind of spider is super-common in houses and can live for many, many years. This can grow up with your kid.”

I’m not sure I’m ready for an in-house pet spider, but while our natural inclination might be to shriek or stamp them out, Dunn wants us to protect them. “The natural enemies of the pests in our homes are very often, whether you like it or not, spiders,” he writes in Never Home Alone: “If you kill the spiders in your home (and this is precisely what we do with many kinds of pesticide applications), you do so at your own expense.”

The curse of pesticides brings us to the bathroom and another key area of his research: shower heads. Dunn and his team asked people from across the US and Europe to send in swabs from their shower heads. And within the biofilm – “a fancy word for the gunk” that builds up inside them – they discovered a pathogen, non-tuberculous mycobacteria (NTM), that is linked to lung disease in people with weak immune systems. What they didn’t know was why this pathogen seemed more prevalent in some regions than others. “There was more of the NTM in the US and in particular in chlorinated water,” says Dunn. They came to the conclusion that “residual chlorine kills all the competing bacteria and just leaves the NTM, which are chlorine-intolerant.” And when the competition is eliminated, the pathogens thrive.

He unscrews the shower head from the hose and runs his finger along the rubber fitting. There is very little biofilm-gunk, which he credits to the quality of the local water supply. “Most of Copenhagen still has untreated groundwater that relies on the wild biodiversity of crustaceans and bacteria to clean it. But if you break that – like we do in the US – it’s super-expensive to fix it and it sucks. And it makes you sick.”


“Yes, in some cases you can encounter small crustaceans in the tap water here. Denmark tastes like biodiversity.”

We continue through the living room and kitchen. He pulls a book from the shelf to test for book lice, and picks up a log of firewood that has a spidery, grey pattern of reindeer lichen growing on the bark. In the kitchen he checks the dishwasher soaptray for a particular form of bacteria that is otherwise only found “in the faeces of tropical fruit bats”. Even our salt jar is apparently full of life: “Almost every crystal of salt has bacteria inside, and when you brine something in salt, those bacteria contribute to the flavours of the brine. The longer it sits in the brine, the more the microbes in the brine are going to contribute to it. Isn’t that cool?”

Food is an area where Dunn has found the influence of microbes and bacteria to be more palatable to people he meets. Food is alive – whether it’s sourdough bread, kimchi or beer – and we are cool with that. Much more so than with the spider crawling across our windowsill. Dunn describes a study of how specific microbes found on bakers’ skin influence sourdough starters and the flavour of bread. His team gathered 15 bakers at a facility in Belgium and tasked each of them with making sourdough starters from identical ingredients. When they tested the bakers’ hands afterwards, it showed a close relationship between the microbial makeup of each starter and the bacteria found on the skin of the baker who made it. In his book Dunn describes how the bakers and biologists, drunk on spontaneously fermented Belgian beer, tucked into the breads and broke into an impromptu toast: “‘To bread, and to microbes!’ And to a house in which both are delicious. ‘To bread and to microbes!’ And houses in which we are all healthy. ‘To bread and to microbes!’ And to lives filled with wild species we have yet to study or understand, species that float like mysteries all around us and offer services we are only beginning to measure.”

Our house tour and inspection has come to an end. I’m curious about the professor’s verdict. Is this a happy, fungi-rich, insect-thriving home? “You have a lot of species that I think of as being part of a healthy house,” Dunn says. “To me, your house is rich in biodiversity and seems dominated by those things that you either shouldn’t worry about, or that are beneficial. Also, I don’t see antimicrobial products all over the place.”

He points to the leftovers of a coffee kombucha-glazed Danish pastry we were eating earlier. “And then you have things that spark joy for you: fermented pastries, salt that’s alive and healthy water from Denmark that we know is alive.”

Whether we like it or not, the species living in our homes are a measure of our lives, says Dunn, and his biggest fear is that we risk killing off that biodiversity. “If spiders scare the hell out of you, but you are willing to have one living in the corner, and maybe approach it sometimes to keep an eye on it, then that’s great. That’s much better than if your response is to jump away from it and spray pesticides all over your home, because that will only favour species that cause us harm and are resistant to pesticides. But it’s not easy. This book won’t solve [the problem], but maybe it will open some new conversations.”

As he says goodbye and walks down the garden path, I spot a tiny moth in our living room, flapping frantically in the corner. I don’t freak out or necessarily feel any great joy, but I leave the moth be. After all, there are 5,000 of us here, and you need to give your housemates some privacy.

Never Home Alone by Rob Dunn is published in the UK by Basic Books (£22.99) on 14 March


A Book That Will Make You Terrified of Your Own House

By Robin Marantz Henig

Dec. 31, 2018

NEVER HOME ALONE: From Microbes to Millipedes, Camel Crickets, and Honeybees, the Natural History of Where We Live

By Rob Dunn

A young man I know used to say that humans have no need to bathe, since our hair and bodies are designed to self-cleanse. I would fight him on it, being of the opinion that washing up occasionally was good for us — and for the people with whom we lived. But now, after reading the entomologist Rob Dunn’s description of the myriad microbial life-forms that take up residence in a typical American showerhead, I’m starting to think maybe that young man was onto something.

With an army of collaborators, Dunn, a professor of applied ecology at North Carolina State University, took samples of the gunk inside hundreds of showerheads, and found a profusion of microbial fauna. Tap water itself, he writes in the chatty, informative “Never Home Alone,” teems with amoebas, bacteria, nematodes and crustaceans. As the water passes through the showerhead, these microbes lay down a kind of scaffolding known as biofilm to protect themselves from getting washed away with every ablution. They make the biofilm “out of their own excretions,” Dunn writes bluntly. “In essence, by working together, the bacteria poop a little indestructible condominium in your pipes.”

It gets worse. Filtered through that poop-biofilm, the water that washes over you, as you supposedly scrub yourself clean, might contain not only all those harmless amoebas and nematodes but a few bacteria that can be dangerous — in particular some species of Mycobacterium, cousins of the Mycobacterium that causes tuberculosis. And the pathogens are there because we provided the perfect breeding ground for them, when we tried to purify our tap water in the first place. Municipal water treatment plants use chlorine and other chemicals that kill off the bacterium’s natural predators, allowing Mycobacterium to thrive. Tap water that comes from a well, in contrast, has never gone through a treatment plant and has a rich microbial life. It might look more dangerous, but it’s actually safer, Dunn explains. All those organisms in well water are themselves harmless, and they tend to fight off the potentially dangerous ones like Mycobacterium — that’s how biodiversity works.

News from the showerhead biome is just one part of this fact-filled, occasionally disgusting, slightly alarming book. Dunn has been involved in an obsessive quest to document the tiny inhabitants of indoor environments, a project that involves teams of professional and amateur bug-watchers to take samples not only from showerheads but from door frames, refrigerators, hot water heaters, cellars, toilets, pillowcases, all sorts of surfaces from the places we call home. These workers swab and seal, swab and seal, and send their thousands of samples to Dunn’s lab in Raleigh, or to his other lab at the Natural History Museum of Denmark, for an ongoing microbial census.

“We expected to find a few hundred species,” Dunn writes of his first foray into indoor microbe-hunting, which involved 1,000 homes from around the world. Instead, he and his colleagues found a “floating, leaping, crawling circus of thousands of species,” perhaps as many as 200,000, many of them previously unknown to science.

These denizens of interior spaces are our most frequent companions. In the industrialized world, we spend upward of 90 percent of our time indoors. Luckily, most of our co-habitators are either benign or actually beneficial in some way, like the house spiders that keep down indoor populations of flies or mosquitoes that can carry disease. But because we’ve become so hyper about making our surroundings as pristine as possible — sealing off our homes from the outdoors and using pesticides and antimicrobials with a vengeance — we’ve tipped the scales away from those harmless or helpful bugs, in favor of some of the bad guys.

According to Dunn, indoor microbes are among the fastest-evolving species on the planet; they have an uncanny ability to live in ecological niches you could hardly imagine existing, like the dead skin cells we slough off every day (which is all that’s needed to survive for a class of bacteria known as detritivores).

They manage to evade our assaults, and evolve their way out of just about every biocide we throw at them. We’re left to contend with the consequences of our own warfare, such as pesticide-resistant German cockroaches and bedbugs, and antibiotic-resistant MRSA bacteria. We have turned a relatively harmless indoor biome into something that can make us sick.

That’s the take-home message of “Never Home Alone,” that the richer the biodiversity in our indoor environment, the better. “The biodiversity of plants and soil can help our immune systems function properly,” Dunn writes. “The biodiversity in our water systems can help keep pathogens in the water in check. … The biodiversity of spiders, parasitoid wasps and centipedes can help control pests. The biodiversity in our houses provides the opportunity, too, for the discovery of enzymes, genes and species useful to all of us, whether to make new kinds of beers or to transform waste into energy.”

I’m not quite as enamored of our microbial roommates as the author is. (I’m sorry, Professor Dunn, but I’m just being honest here: Those photos of the camel cricket and the American grass spider clinging to basement pipes and door thresholds — well, yuck.) It probably takes the soul of an entomologist, or maybe of a 9-year-old child, to love these bugs as much as Dunn does. Still, it’s hard not to be occasionally charmed by his prose, as when he catalogs the arthropods with whom we share our homes: “biting midges, mosquitoes, lesser house flies, phantom midges, freeloader flies and shore flies. This is not to mention fungus gnats, moth flies and flesh flies. Or crane flies, winter crane flies and minute black scavenger flies.” And it’s hard not to share, at least a little, his awe at their diversity, even in a single household. “If you see two flies in your home,” he writes, “the odds are that they are two different species. Heck, if you see 10 flies in your house, they are likely to be five different species.”

And don’t even get him started on the aphids. He’s amazed by them, as he is by “the wasps that lay their eggs in the bodies of aphids as well as the wasps that lay their eggs in the bodies of the wasps that lay their eggs in the bodies of aphids.”

There’s a real sense of “gee-whiz” in this book, but it’s mostly in service of Dunn’s overarching goal: to preach the preservation of biodiversity, not only in the lush forests and streams that fit our traditional image of nature’s abundance, but in the most humble places, too, where the vast majority of us will have most of our cross-species encounters — our basements, mattresses, refrigerator drawers and showerheads.

About those showerheads: Dunn isn’t suggesting that we give up showers. But he does say we might want to change the showerhead a little more often — and consider switching from metal to plastic, where biofilm is less likely to accumulate. Nonetheless, his bottom line for showerheads is like his bottom line for other aspects of the roiling microbial mix we live in: Don’t be afraid of letting life inside. “The water that is healthiest for bathing is that which comes from aquifers rich with underground biodiversity including crustaceans,” he writes. “The crustaceans in these aquifers are an indication not of the dirtiness of the water but of its health.”


Robin Marantz Henig is a New York science journalist whose books include “The Monk in the Garden: The Lost and Found Genius of Gregor Mendel.”

About Bruce

Work for sustainable development of small islands and the Chesapeake Bay; ex-Peace Corps (Volunteer and staff) in LA & Caribbean; cruised Caribbean on S/Y Meander for three years; like small tropical islands, French canals, Umbria, Tasmania, and NZ. Married 52 years to the late Kincey Burdett Potter (see President of the now-sunsetting Island Resources Foundation.
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