Forget the rain forest—your home is brimming with bugs. More than 500 kinds of them.

Spiders, flies, beetles, ants, and book lice are among the critters detected in a new study, the first to evaluate arthropod diversity in U.S. homes.

Arthropods—a huge group that includes insects, spiders, and their relatives—have been living and evolving alongside people for millennia. (See "Why Did Thousands of Venomous Spiders Swarm a House?")

“Nobody had done a comprehensive inventory like this before, and we found far more diversity than most people would expect," says study leader Matt Bertone, an entomologist at North Carolina State University.

“That old wives’ tale that you’re never more than ten feet [three meters] away from a spider? If you’re in your home, that might be true,” Bertone says: His team found spiders in all of the homes surveyed.

Home is Where the Bugs Are

For the study, Bertone and colleagues visited 50 free-standing houses in and around Raleigh, North Carolina.

“We had two or three entomologists searching the houses, crawling on our hands and knees with flashlights and collecting anything we could find into vials,” says Bertone. The researchers collected their samples, both living and dead, using forceps, aspirators—a type of vacuum—and nets.

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Bertone and his colleagues gathered over 10,000 specimens, representing over 300 families of arthropods, and conservatively, 579 species. Each house was home to anywhere between 32 and 211 arthropod species, according to the study, published January 19 in the journal Peer J.

In addition to the sheer number of species, the researchers were surprised at how many bugs they found in the homes. Out of more than 550 rooms sampled, only five were totally bugless. (See "7 Bug and Spider Myths Squashed.")

Although some of the species have adapted to live happily alongside humans, such as book lice, others, such as leafhoppers and gall midges, are accidental visitors. These bugs simply wander in from the outdoors and can become trapped and die, the study authors say.

Peaceful Cohabitators

There are probably even more bugs in our homes, since the researchers only collected arthropods from visible surfaces, excluding areas such as behind walls, under heavy furniture, and in drawers and cabinets, Bertone says.

But he emphasizes that we shouldn't be afraid of the bugs in our midst—the vast majority are not harmful. Typical household pests, such as German cockroaches, termites, and fleas, were only present in a few homes, the survey found. And those ubiquitous spiders found in every home are very benign—not to mention they eat pests. (Related: "What Should You Do If You Find a Spider in Your House?")

“My take-home message to the homeowners was that these things are living among you but they’re not dangerous and you won’t see them unless you really look for them,” says Bertone. “They are peacefully cohabitating with us.”

Jason Cryan, an entomologist at the North Carolina Museum of Natural Sciences, says he's "not bothered by the fact that they are finding so much arthropod diversity in our homes."

“In many cases this diversity goes unseen and unheard,” says Cryan, who was not involved in the study.

“I hope people will appreciate this natural diversity and realize that this life among us is not a health or a cleanliness concern.”