colorful dollhouse interior

Your home could be the most interesting biome yet. (Photo: Robert Kneschke/Shutterstock)

Who shares your home with you? And we're not talking about partners or children; we mean the other organisms that live in your personal space.

When you think of a biome, you probably think of the rain forest or the desert. But researchers say the fastest-growing biome is actually the indoor environment.

According to a new study from researchers at Cornell University, the indoor biome makes up about 0.5 percent of ice-free land, or about 247,000 square miles, which is nearly the size of Texas.

“People have this picture that there are only a few insect species and microbial species eating human scrap,” says Cornell graduate student and researcher Laura Martin. “But given the number of species found indoors, it is likely there’s a lot more going on that we don’t know about.”

That means that other than your dog, cat or the occasional ant invasion, there are maybe hundreds more species (and millions of microbes) sharing our living spaces.

Since humans began building homes about 20,000 years ago, all sorts of critters moved in right along with us. The indoor biome has grown to colossal proportions and, as a recent New York Times article points out, with the advent of elevators and other technology, it's still growing upward toward the sky.

So what's in there?

Researchers in the Cornell study took a seriously close look at 40 homes in North Carolina. They documented more than 8,000 varieties of bacteria and microorganisms. In the same state, another study of 50 houses found more than 750 types of arthropods, including spiders and insects. A smaller look at 11 houses in California found an impressive array of fungus.

Just like humans pick and choose where they want to live, your microscopic roommates also have residential preferences.

According to the University of Colorado Boulder microbiologist Noah Fierer, the greatest biodiversity hotspot in the kitchen is the stove exhaust vent, likely due to forced air and settling.

According to The New York Times, Fierer's lab scrutinized 82 surfaces in four Boulder kitchens. There was evidence of soil on the floor and species linked with raw produce on the countertops. Microbes were living above the faucet and bacterial species associated with human skin were the top residents.

“The radical diversity in abiotic environments, such as in water heaters, freezers, and on kitchen counters, is vast and could parallel microclimates found on forest floors,” says Martin.

The point here isn't to freak you out — it's to open the door for a whole new realm of science to explore. What can we learn from these microorganisms? How fast do they grow?

“We are interested in reframing the dialogue away from what gross or dangerous pests live in houses to what biodiversity exists in houses.”

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Mary Jo DiLonardo Mary Jo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.