Meet the bugs that call your house home

If you’re one of those people who can’t stand finding even the most harmless bug inside your house and kills the spiders that prey on everything else, you might not want to read this. That’s because despite your best efforts to eliminate every creepy-crawly from view, there’s probably plenty more hanging out in your home.

The good news is that the vast majority of arthropods found inside houses in a recent census were not pests. The bad news — at least for the entomophobes — is that no home was completely free of insects or arachnids, and only five out of 554 rooms sampled were totally clean.

Those results come from the first-ever census of arthropod diversity in homes, published January 19 in PeerJ. To conduct the survey, Matthew Bertone of North Carolina State University in Raleigh and colleagues visited 50 homes around Raleigh in 2012 and collected any living or dead arthropods that they could find in plain sight, including those hanging on spiderwebs. They also vacuumed up a small patch in the center of every master bedroom to look for dust mites. Then they brought their samples back into the lab and, to the best of their ability, identified the more than 10,000 specimens they collected.

“We found that an individual house may have hundreds of arthropod species within it,” the researchers write. On average, each house contained 62 families and at least 93 species. Some had 500 species or more. Bigger homes tended to have more species than smaller homes. “Many species we found were unexpected, unnoticed by residents until they were collected, and play no pestiferous role in human houses,” they write.

Every home had cobweb spiders, carpet beetles, ants and gall midges (tiny flies whose larvae feed inside plant tissue). Nearly every house had dark-winged fungus gnats and book lice, which eat fungus or mold (not books). Three-quarters had dust mites.

Pest species — the subject of most studies on arthropods found inside homes — were actually pretty rare. Only 6 percent of homes had German cockroaches, 10 percent had fleas and 28 percent had termites. None had bedbugs.

Some of the arthropod species were synanthropic, meaning that they have evolved to live near humans. But many just wandered in from the outside or were carried in by accident, such as on a bouquet of flowers. Many of those species don’t last long indoors, but their carcasses remain.

While these results are interesting, it’s difficult to say how applicable they are to homes outside the Raleigh region. And the findings bring up a host of new questions: How much does geography matter to what lives inside your home? Does cleanliness or the type of surfaces — such as carpet or hardwood floors — play a role? Does time of year matter? Do pets increase arthropod biodiversity?

In addition, the researchers didn’t search out any arthropods that may have been hiding inside drawers, behind furniture, around baseboards or ceilings or inside walls. Thus, this study provides only a hint of the true biodiversity found within our homes.

So if you’re ever feeling lonely, just remember, you’re probably not alone. You just have to look around.