"They're our present, but often-ignored roommates."
Madden and her colleagues solicited samples from more than 700 houses in all 48 contiguous states. Each contributor needed to provide only a tiny amount of dust -- one swab from inside the house, another from outside. Each sample could fit on the head of a cotton bud.
But contained within those swatches of dust was a world of knowledge. After all, dust isn't just dust: It's microscopic detritus of the ecosystem that is your home. It's got bits of bug leg and moth wing scales, flakes of your skin and dander from your pets, bits of faeces from inhabitants large and small (hope you weren't still eating breakfast). By sequencing the DNA of the organic material in each sample, Madden could conduct a genetic census of the creatures in that household.
For this study, she focused on the arthropods. She was specifically interested in analysing the diversity of bugs - the variety of standard and surprising creatures living among us. Some households she examined had representatives from as many as 45 genera. (Note that diversity is different from abundance: Just because these houses had a wide assortment of bugs doesn't mean they were overrun with insects.)
These results allowed researchers to understand the complex interactions that take place unnoticed at our feet and within our walls. For example, many samples contained DNA from tiny plant-eating aphids, ladybugs that eat them, and parasitic wasps that lay their eggs in aphids.
"We're seeing entire food webs," Madden said.
"Parasitoids, predators and prey all existing in dust."
She and her colleagues also began to pick out some trends in the distribution of arthropods and the kinds of homes they like to live in. Roaches tended to stay in warm climates, whereas ladybugs were more plentiful in cooler locations. Dust mites like humidity. Houses with pets tended to have more diverse bugs, as did ones with basements.
This data could help clinicians working to understand things such as allergies, according to Madden. It's known that dust mites are a common cause of asthma, as is cockroach waste.
"It's good to think about what unexpected arthropods we might be interacting with to figure out how they might be affecting our health in the future," Madden said.
Some of our bugs may make our homes better without us noticing -- spiders that eat other pests, for example.
Some might be accidental intruders, tracked in on a sleeve or a dog's paw and as eager to escape the carpeted confines of our homes as we are to kick them out.
Still others may carry out their entire existences right next to us, without us ever noticing.
"It's fun to reveal the mysteries that we didn't even know were mysteries," Madden said.
"We think of our houses as our most well-known and intimate habitats, and yet we still have so much to learn about what's going on inside of them."
