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A wide diversity of bugs share our homes with us — no matter how tidy we are, study finds

Study: “Cellar spiders are relatively large arthropods, so perhaps they would be less likely to accumulate in tidier houses, and cluttered areas may offer more structures on which they can build their webs.”

Our homes are havens for a diverse group of creepy-crawly bugs — whether or not we keep the place tidy, or use pesticides, or own a cat or dog.

That’s the key take-away message from a fascinating study published last Friday in the journal Scientific Reports.

“We are just beginning to realize — and study — how the home we create for ourselves also builds a complex, indoor habitat for bugs and other life,” said Misha Leong, the study’s lead author and a postdoctoral researcher at the California Academy of Sciences, in a released statement. “We’re hoping to better understand this age-old coexistence, and how it may impact our physical and mental well-being.” 

If you’re grossed out by the thought of a host of different kinds of bugs crawling unseen (mostly) around your rooms, don’t be. As Leong and her colleagues point out in their paper, the idea that we share our homes with “uninvited biodiversity may not seem appealing, yet a growing body of evidence suggests that many of our chronic, modern diseases are associated with our failure to be exposed to biological diversity, particularly that of microbes, some that may be vectored [carried inside] by insects.”

“In this light, rooms with more kinds of [bugs] may well be healthier rooms,” they add.

Thousands of specimens

For the study, the researchers painstakingly collected and cataloged living and dead arthropods  — more than 10,000 specimens in all — from nooks and crannies in 50 homes within a 40-mile radius of Raleigh, North Carolina.

Arthropods are invertebrate (spineless) animals with an external skeleton, a segmented body and jointed appendages. They include insects, as well as close relatives like spiders, mites and millipedes.

The researchers were interested in diversity rather than quantity. The specimens collected comprised 304 unique arthropod families. There were between 24 and 128 different families, and between 32 and 211 different species, of the creatures in each house.

Pets and mess not factors

Leong and her colleagues then examined how different physical features within the homes, as well as certain lifestyle factors, influenced the diversity and composition of the arthropods found.

In terms of lifestyle, the data revealed that the presence of cats or dogs, the number of houseplants, the use of pesticides and the tidiness or messiness of a house made no significant difference in either the diversity or composition of the arthropods found.

“The only significant relationship we found with house variables was that more cluttered house had slightly higher proportional occurrences … of cellar spiders,” the researchers write. “… Cellar spiders are relatively large arthropods, so perhaps they would be less likely to accumulate in tidier houses, and cluttered areas may offer more structures on which they can build their webs.”

Although the scientists didn’t find a significant difference in arthropod diversity between pet and non-pet households, they did uncover an interesting difference between houses with cats and those with dogs.

“There was a trend toward greater arthropod diversity in houses with dogs and, intriguingly, reduced arthropod diversity in houses with cats,” the researchers write. 

“While our data does not differentiate between outdoor and indoor house cats, reduced arthropod diversity could be due to cats actively hunting arthropods indoors,” they add.

More windows, more diversity

Here’s a summary of what the data revealed regarding a home’s physical features and its arthropod diversity:

  • Large common rooms, like living rooms and basements, had a greater diversity of arthropods than more specialized rooms, such as kitchens and bathrooms — most likely because they tended to be more accessible to the outside.  “Overall, as the number of doors and windows increased in a room, so too did the arthropod diversity,” the researchers explain.
  • The diversity of arthropods in rooms also tended to decrease the higher the floor level. Again, this finding is probably related to the fact that upstairs rooms tend to have fewer windows. 
  • Carpeted rooms also had more arthropod diversity than those with bare floors. Some bugs, like dust mites, actually live in carpets, but rugs “may also act as a trap for many arthropods, regardless of their normal habitat inside or outside of the house,” the researchers write.
  • Not unexpectedly, basements and crawl spaces tended to have the most unique composition of arthropods, probably because of their subterranean location, low light levels and high humidity, say the researchers. Bugs underrepresented in the study’s basements were those that fly — flies, moths and wasps — as well as jumping spiders, which rely on visual skills for hunting. “Surprisingly, silverfish (Lepismatidae) and booklice (liposcelididae) were also underrepresented in basements where they would be expected to thrive based on the damp environment they are thought to prefer,” the researchers add.
  • Many of the most dreaded indoor pests — termites, fleas and bed bugs — were relatively rare among the bugs collected in the study.

‘Wild ecological dramas’

Of course, the study collected insects, spiders and other arthropods from homes in a specific geographical area. If the collection was done elsewhere (say, here in Minnesota) the results — certainly the results concerning the composition of the arthropods collected — would have been different.

Still, the study’s findings suggest, as Leong and her colleagues write in their paper, “that indoor arthropods serve as a connection to the outdoors, and that there is still much yet to be discovered about their impact on indoor health and the unique ecological dynamics within our homes.”

“Even though we like to think of our homes as shielded from the outdoors, wild ecological dramas may be unfolding right beside us as we go about our daily lives,” said Leong. “We’re learning more and more about these sometimes-invisible relationships and how the homes we choose for ourselves also foster indoor ecosystems all their own.”

FMI: You can read the study in full on Scientific Reports’ website.

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