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Scientists survey 50 Americans homes, find more than 500 kinds of arthropods

  • In the first study of its kind, a team of entomologists scanned a total of 554 rooms in 50 homes in Raleigh, U.S., and collected arthropod specimens from all visible surfaces, including under and behind furniture, around baseboards, ceilings, shelves, and inside closets.
  • The surveys resulted in a haul of over 10,000 arthropod specimens belonging to 304 different families.
  • Typical household pests were either uncommon or totally absent from the homes, suggesting that the majority of bugs found in homes are not direct pests and do nothing but exist alongside us, researcher says.

If you think your home is free of bugs, think again. A new study has found that arthropods — a group of animals that have an external skeleton and jointed legs — thrive in U.S. homes. In fact, American homes can have more than 500 different kinds of flies, spiders, beetles, wasps and other arthropods. But most of these bugs are harmless, the study published yesterday in PeerJ has found. Many bugs are cryptic, and so unknown to the average homeowner.

In the first study of its kind, Matthew A. Bertone of North Carolina State University in Raleigh, North Carolina, and his colleagues, surveyed 50 free-standing homes in Raleigh and neighboring areas of North Carolina in the U.S. for arthropods.

The team of entomologists scanned a total of 554 rooms in the 50 homes — including attics, basements, bedrooms, common rooms, and kitchens — and collected arthropod specimens from all visible surfaces, including under and behind furniture, around baseboards, ceilings, shelves, and inside closets. They also collected dust mites from the master bedroom floor using a modified vacuum.

The team however, did not sample external parts of the homes, such as screened porches, decks, garages, detached sheds or structures, and closets that are accessible only from the outside.

“Nobody had done an exhaustive inventory like this one,” Bertone said in a statement. “Most studies focus on one type of arthropod, and typically pests. But we knew there were many examples of such animals living with us and we wanted to see what that looked like across many homes,” he told Mongabay.

Ants were one of the most common arthropods in the 50 homes. Photo by Matthew Bertone.

The surveys resulted in a haul of over 10,000 arthropod specimens. Only five of the 554 rooms sampled did not have any arthropods.

Bertone and his team identified and grouped the bugs, and found that there were at least 579 different kinds of arthropods in the 50 homes from 304 different families. Each home had 32 to 211 arthropod species, belonging to 24 to 128 families.

The true diversity among these 50 homes is undoubtedly much higher, the authors write in the paper. This is because the team could have missed many cryptic species during their surveys. Moreover, the team did not sample areas behind walls, under heavy furniture, and in drawers and cabinets, all of which could have been hiding additional arthropods, they add.

Of the 10,000 arthropods sampled, some were more common than others. For example, all 50 homes, the team found, had cobweb spiders, carpet beetles, gall midge flies, and ants. Nearly all homes (over 96 percent) also had book lice and dark-winged fungus gnats. And over 80 percent of the homes shared true flies, fungus gnats, mosquitoes, scuttle flies, non-biting midges, and gall midges.

“I was surprised to find over 10,000 specimens in the 50 homes, as well as the fact that several groups could be found in 100 percent of the homes,” Bertone said. “I was also surprised that cobweb spiders were found in 65 percent of rooms — more than I thought would be the case.”

Proportional diversity of arthropod orders across all rooms. Photo by Matthew Bertone.

American homes seem to be teeming with arthropods of various kinds. So why don’t we see them more frequently? It could be because many arthropods are either very small, or lead a cryptic lifestyle, Bertone said. We also either don’t look hard enough for them, or the bugs are so obscure that only experts know what they look like, Bertone told the Atlantic.

Despite the surprisingly large diversity of arthropods in the 50 homes, most were harmless, the team found.

Typical household pests were either uncommon or totally absent from the homes. For instance, the team found German cockroaches in only six percent of the homes, and fleas in only 10 percent of the homes. A major household pest, the bed bug, seemed to be totally absent.

“Although we did find some pests, like those that infest stored food products or may damage clothing and other textiles, we did not find many of the pest species of cockroaches, fleas or any bed bugs,” Bertone said. “The lack of many major pests could be because we sampled certain types of homes and did not sample places like apartments in the city, where we might expect to find more pests.”

In fact, pest species were less common than many other cryptic and harmless arthropods. Bugs like cobweb spiders are typically peaceful co-habitants, for example, while midges and leafhoppers, are often accidental visitors, the authors write.

“This suggests that the majority of things found in homes are not direct pests and do nothing but exist alongside us,” Bertone said. “Many arthropods have been living alongside us and most people are unaware that they are there.”

Moreover, Bertone cautions that while his team collected hundreds of bugs from each home, it does not necessarily mean that all the sampled bugs actually live inside the homes.

“Many of the arthropods we found had come into the homes accidentally and ended up dying,” he said. “Thus, for the short amount of time they exist in our homes they are likely not affecting us in any way.”

For instance, the team found gall midge flies in all 50 homes. But these flies feed on plants outside, and cannot survive indoors.

Ground beetles, such as this false bombardier beetle (Galerita sp.), are happy out in nature, but will often wander into homes and roam around looking for prey (or a way to make it back outside). Photo by Matthew Bertone.

Arthropods, one of the most successful groups of animals on earth, thrive in our homes. Yet, the average homeowner is oblivious to most of them because the bugs go about their lives in secrecy, Bertone said.

“Many are small to tiny, and often hide from humans,” he said. “They are not affecting us in any major way and may be providing benefits we don’t know about – for example, feeding on true pests.”

However, this study is only preliminary, and more work needs to be done to flesh the picture out, co-author Michelle Trautwein of California Academy of Sciences said in a statement.

“But these insights give us the opportunity delve down into some exciting scientific questions,” Trautwein said. “Do they provide important services that we don’t know about in the ecosystems of our homes? We can also begin to explore their traits to see if they share evolutionary characteristics that have made them better suited to live with humans.”

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