beetle
© Matt BertoneFalse bombardier beetle
You may think your home is your castle, protected from animal invaders by cleaning products, sealed windows, doors, and walls. But scientists who have conducted the world's first survey of arthropods—creepy crawlies like insects, spiders, mites, and centipedes—in U.S. homes, report otherwise.

They randomly sampled the arthropod community in 50 homes in Raleigh, North Carolina, in 2012. The houses ranged in age from 7 to 94 years old, and from 840 to 4833 square feet. Armed with forceps, aspirators, and butterfly nets, the scientists hand-collected specimens—living and dead—from each room. They searched under and behind furniture, along baseboards, ceilings, on shelves, and in closets, amassing a collection of more than 10,000 specimens.

They gathered at least 579 morphospecies—animal types that are difficult to precisely identify—from 304 families. Flies were the most abundant, followed by spiders, beetles, ants, and book lice, whereas fleas and the American cockroach were relatively rare, the scientists report in today's issue of PeerJ.

Some of these, such as the book lice, have a long evolutionary history of living with humans. But the vast majority of specimens were inadvertent visitors, such as gall midges, leafhoppers, and ground beetles (like the false bombardier beetle, pictured above), who had wandered in and were likely looking for the exit.