Beneficial bugs and the drawbacks of cleanliness

As much as you try and clean your house, the pests are always going to come back...
24 February 2022



Allan Duffie wants to know about ants in his home and what he can do about them, 'Are these benign freeloaders or seriously unwanted guests?'


Rob - In most people's houses they're just an interesting part of the natural world and, in most cases, the pesticides you would use to kill them are far less benign than the ants themselves.

Chris - When you mention this whole business about cleaning products, can we actually see the impact?

Rob - I think we're aware of some of the ways we change the habitats around us. We're aware of when the birds change - we no longer hear the same sounds, we're aware of when the plants change - we don't see the same flowers. Hidden in those stories is the fact that we're fundamentally changing how all these pieces of nature work together. Most of the food the animals and cities are eating is actually coming from human waste streams, and if you pick up an ant in New York City, in Manhattan, most of its carbon molecules actually come from corn syrup and from eating animals that have been fed corn. The other thing that we know is that we're triggering totally different evolutionary scenarios: what we now know is that where evolution proceeds most quickly is in habitats that are becoming ever bigger and where the selection pressures are really strong. That's exactly what we've created in cities. And so, there's an underground mosquito in the tube, in London, that appears to be part of a lineage that specialised for tubes and subways. The rats on the South end of Manhattan are diverging from the ones on the North end of Manhattan; the bacteria and other smaller species are evolving even more rapidly - and so they evolve in response to an individual course of antibiotics. I think we look outside and we see something that seems static but, in fact, this evolutionary story is faster than it's been in a long time in many ways.

Chris - Are the houses that we are making these days a bit too clean for our own good?

Rob - That's for sure. We're coming to understand that we need exposure to certain species to be healthy. Now, which species we need to be exposed to is a very complex question, because it's at the interface of the immune system. But, we do see that as people spend more and more time inside, and their houses are more and more clean, that there are a whole series of broader immune problems that arise: these are skin problems, it's gut problems, it's brain inflammation problems that seem to be associated with these changes. There's been a push now to think about, "Well, what do we need to bring back into our daily lives to restore some kind of a balance?" And it's a tricky question. What the companies want to do is to give you a pill that has the particular microbe we need. What some ecologists want to do is to imagine restoring more biodiversity to our daily worlds, and to get us outside more. It's a tricky time. We know there's a problem, but the solution is not fully apparent yet.

Chris - No danger of my house being too clean. But, if everyone was like me, what microbes will be taking over first? If we all stopped obsessively cleaning, what would dominate?

Rob - I'll answer the opposite question first: the international space station is a perfect experiment in what happens if you try to seal everything out and clean really well. In that environment, you mostly get microbes associated with the body because the body's constantly falling apart and so the international space station is full of those microbes. Then you get extreme loving microbes; things that can grow on metal, on plastic. At one point, the windows and mirror of the Russian space station were so covered in fungus that they could no longer see outside, and so the universe was obscured by the grandeur of life. The other extreme is what happens if you open your windows? What happens if you live in a house that has more continuity with the outside world while soil microbes come in, leaf microbes, come in the insects that come in, bring in microbes by and large, those are either benign or beneficial sorts of species.


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