The world’s first “great indoors” survey of arthropods – that’s insects, spiders, centipedes, and friends – revealed that houses in the U.S. are home to hundreds of different kinds of arthropods. As expected, flies, spiders, beetles, and ants were found in nearly every home studied, but surprisingly, most true pests were far less common than inconspicuous, harmless little creepy crawlies. The findings are published in PeerJ this week. 

Arthropods have been evolving with us since the very beginning. Blood-feeding kissing bugs lived alongside our ancestors 26,000 years ago, for example, and among the first examples of cave art is a depiction of a camel cricket. As our societies changed over time, arthropods continued to use us for food and shelter. Yet how much do we actually know about our frequent, uninvited guests? Previous work on indoor arthropods has focused almost exclusively on pests. 

A team led by North Carolina State’s Matthew Bertone surveyed the indoor biome of 50 free-standing homes in and around Raleigh, North Carolina. These houses ranged in size between 78 to 449 square meters (840 to 4,833 square feet) and in age from seven to 94 years old. During a single visit to each house between May and October 2012, the team visually inspected each room and collected all arthropods (living and dead) using forceps, aspirators, nets, and vacuums. They only sampled from visible surfaces, including spaces under and behind furniture, around baseboards, and on ceilings and shelves. When they couldn’t identify the species (because of damage or unidentifiable life stage, for example), the team classified the specimens by what's called morphospecies. 

The team discovered incredibly high diversity: a conservative range of 32 to 211 species or morphospecies from 24 to 128 distinct arthropod families per house – or 93.14 on average. In total, the 10,000 specimens they collected spanned at least 579 morphospecies from 304 arthropod families. The majority of this indoor diversity (73 percent) consisted of four groups: flies, spiders, beetles, and wasps and ants. 

Many had filtered in from the surrounding landscape, and because of this, common pest species were uncovered far less frequently than benign ones. German cockroaches, subterranean termites, fleas, bed bugs, and even large American cockroaches were found in only a minority of the homes. Mosquitoes and smoky brown roaches, on the other hand, were quite common, just like pillbugs and springtails. And despite how surprisingly common they are, gall midges, book lice, and dark-winged fungus gnats are unfamiliar to the general public. Better-known insects, like moths and butterflies, were collected infrequently. 

While houses today host many of the same pest groups (like grain beetles) found in archaeological sites, today’s arthropod communities do reflect modernization. With the advent of indoor plumbing, dung beetles aren’t found inside as much, whereas drain-dwelling moth flies are. Meanwhile, species that are closely associated with us and our homes – like house flies, fruit flies, and German cockroaches – have gone global. Some species even lack populations in the wild.