Meet your creepy-crawly roommates

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The average U.S. home contains almost 100 distinct kinds of arthropods, a diverse group of animals that have exoskeletons and segmented bodies and include insects, spiders, and centipedes, according to a study published today in PeerJ.

But don’t let the mere thought of all those bugs make you itchy: most of these creatures appear to be harmless, scientists say.

Researchers visited 50 free-standing homes in the Raleigh, North Carolina area between May and October 2012. They collected all the arthropods they could find – living or dead – from kitchens, bedrooms, bathrooms, laundry rooms, and common areas like living and dining rooms. They also conducted more limited sampling of attics and crawl spaces.

The study is the first systematic survey of arthropods in modern homes. “Nobody has done an exhaustive inventory like this one, and we found that our homes host far more biodiversity than most people would expect,” says entomologist Matt Bertone of North Carolina State University.

Altogether, the researchers identified 579 different morphospecies of arthropod belonging to 304 families. A morphospecies is a distinct type of organism that can be readily identified based on the shape and size of its body parts. (Some arthropods, notoriously spiders, are fiendishly difficult to identify to a true species level.)

Arthropods in our homes are not only diverse but ubiquitous. The researchers found arthropods in all but five of the 554 rooms they sampled.

Individual houses contained an average of about 93 morphospecies belonging to 62 arthropod families. Because of the specific sampling and calculation techniques used, these are probably conservative estimates, the researchers say.

McMansion dwellers had better not be squeamish: the researchers found that bigger homes contained more kinds of arthropods.

All of the houses in the study hosted cobweb spiders, carpet beetles (which the researchers found feeding on dog kibble, dead insects, and fingernail clippings), gall midge flies, and ants. All but one or two had book lice and fungus gnats.

Most studies of arthropods in human homes have focused on harmful species. But the new study found only a minority of houses inhabited by pests like German cockroaches (6%), termites (28%), and fleas (10%).

Some of the arthropods found in houses, like leafhoppers, gall midges, and click beetles, are merely visiting. They waft in as “air plankton” or get introduced by accident on cut flowers or fresh produce. What’s home sweet home to us is actually a trap to them: and if they don’t get out soon, they die.

But other species, like cobweb spiders, are adapted to living with humans and are more or less permanent co-residents. We’ve been living with arthropods throughout our evolutionary history, after all, and by now some species have become globalized along with us (fruit flies), and some even lack “wild” populations altogether (German cockroaches).

In the new study, researchers found a number of species in modern homes that have also been identified in archaeological sites: grain weevils, grain beetles, carpet beetles, house flies. Of course, as human dwellings have changed, the arthropod fauna associated with them has also shifted: fewer dung beetles, more drain flies.

Arthropods in North Carolina homes include scavengers like silverfish and book lice, predators like spitting spiders and centipedes, and parasitoid wasps that lay their eggs in the bodies of other insects. But very little is known about the structure and function of the food webs inside our houses.

“Now that we have a better idea of which species are most common in homes, we can focus on studying them,” says coauthor Michelle Trautwein, a fly expert at the California Academy of Sciences. “Do they provide important services that we don’t know about in the ecoystems of our homes? Do any host microbial organisms that affect our health, for good or bad?”

The findings contribute to a new understanding that biodiversity in urban areas is greater than was once thought. They also extend the growing appreciation for the variety of organisms that our own bodies host. Our skin has an ecosystem, and now so do our houses – ideas that are weaving us, and our habitats, more tightly into the web of life. – Sarah DeWeerdt | January 19, 2016

Source: Bertone M.A. et al. “Arthropods of the great indoors: characterizing diversity inside urban and suburban homes.” PeerJ DOI: 10.7717/peerj.1582

Header image: Little black ants (Monomorium minimum) investigate a crumb on a couch in a Raleigh, North Carolina-area home. They share the home with an average of roughly 100 other kinds of arthropods, as well as humans. Credit: Matt Bertone.