Uninvited Guests

Features - Cover Story

Researchers found MORE THAN 600 genera of arthropods inside people’s homes. Will that freak out your customers? It shouldn’t. Here’s what you need to know.

October 8, 2018

Illustration by David Leonard

We’re surrounded. They’re everywhere. Our customers’ homes may appear to be squeaky clean, or at least in good enough shape to host a family dinner, but there are hundreds of “party guests” hanging out inside with the humans. They’re not big, loud or messy. And we’re guessing your customers have no idea they stopped in.

They’re arthropods. You know, invertebrates that include insects, spiders and various other creepy crawlies.

“We share our spaces with many different species, and we are only beginning to understand what those species are,” says microbiologist Anne Madden, Ph.D., a researcher at North Carolina State University’s (NCSU) Rob R. Dunn Laboratory. She is the lead author of “The diversity of arthropods in homes across the United States as determined by environmental DNA analyses,” which was published in the journal Molecular Ecology. NCSU and the University of Colorado Boulder collaborated on a study of arthropods in the home, soliciting samples from more than 700 houses in 48 states. Citizen scientists provided a swab of dust from inside the home, and a sample from the outside.

The dust collected tells a dynamic story about the ecology of our homes — and the reality that our inside spaces are not so much a shelter from life outdoors, but actually a robust environment housing more than 600 different types of arthropods. “The study was not about biodiversity that is in a jungle — but biodiversity in our homes and backyards,” Madden relates, noting that their research looked at the number of species (not number of insects). “When most people are concerned about pests in their homes, they are not concerned about diversity. They are concerned because they have a lot of carpenter ants or a lot of bed bugs or cockroaches. We uncovered species that might be existing with us in our spaces, and are probably ignored. Some may not even affect us.”

For example, microscopic wasps get caught in our homes. “They may not live out their entire lives indoors,” Madden says. Many of the arthropods living among us would love to be evicted from the home environment. They show up on accident, riding in on a child’s backpack or wandering through cracks and crevices. They have no idea they’re headed toward a cushy life of carpeting, upholstery and perhaps some stray crumbs from the table.

Other species like dust mites, which showed up more often in humid regions, can be an allergy threat for some individuals. And, of course, there were plenty of nuisance flies and spiders that popped on the radar of researchers. It’s not a bad thing. Spiders, we know, are pest management professionals in their own right, snacking on some other arthropods.

“Most of the time, and this study bears it out, the ‘pests’ or arthropods in question are just an introduction,” says entomologist Jim Fredericks, Ph.D., vice president, technical and regulatory affairs, National Pest Management Association. “Arthropods are not only in the outside world, they are also present in our homes, and I don’t think that’s something that needs to be feared. Instead, it needs to be respected.”

WHAT’S IN THE DUST? So, how exactly do you find out there are 600 different buggers living in your home from a Q-tip sized sample of dust? There were a couple of strategies in place for this research that allowed scientists to find out about the creatures living amongst us.

For one, citizens’ willingness to collect their own samples to send in to the lab removed common barriers to performing this type of discovery, Madden says. Usually, collecting samples from a home means trained entomologists, working on their hands and knees, wearing head lamps and gear. It can feel a tad invasive for homeowners. Not to mention, who wants to have a perfect stranger collecting dust from all of the corners you’d prefer to ignore?

This study asked people to bag up their own dust (just a little bit of it) and invited them to get involved in the process. “It was a great opportunity to show citizens the excitement of scientific discovery,” Madden says. “The citizen science initiative allowed people to be directly involved in the research. Often, it takes a long chain of discovery with many labs and analysis and tools. I like being able to connect with people who are not professional scientists and hopefully show them the relevance of science.”

Madden adds, “Citizens can help us sample in ways we couldn’t do on our own.” The study included samples from 48 states — thanks to citizen participants. Otherwise, the map created might have been regional.

Another aspect of the study is how samples were analyzed, using high-throughput DNA analysis to identify every genus of arthropod present in the dust collected. The advanced DNA sequencing-based approach involves using robotics, data-processing software, sensitive detectors and screening so millions of tests can be conducted pronto. “Our goal was to further develop a molecular method that would allow us to gather a swab of dust and particles of DNA left behind to catalog a list of species that exists in people’s homes,” Madden says.

Scanning electron micrograph of home dust including dust mites, animal fur, fibers and pollen.
Anne A. Madden, with the assistance from Robert Mcgugan at the University of Colorado, Boulder Nanomaterials Characterization Facility. False-coloring done by Robin Hacker-Cary.

The findings were fascinating. For one, there are complex interactions that happen at home without us even realizing it. Many samples of DNA included tiny plant-eating aphids, ladybugs that eat them and parasitic wasps that lay their eggs in aphids — a circle of life. This robust ecology is invisible to most of us. And, it’s really pretty neat. (Arthropod diversity is good.)

Mapping the arthropod genera uncovered interesting trends. For one, dust mites were more likely to be present in homes located in humid regions. Ladybugs prefer northern homes. Turkestan cockroaches have branched out from their Southwest comfort zones and were present in the Northeast. “We found evidence of spiders and other insects that might be passing through the house,” Madden says.

“I hope that our study inspires people to find out more about the life around them, rather than being afraid,” Madden says. “By learning more, we can start to understand which arthropods could be pests.”

‘PESTS’: THINK DIFFERENT. “There was a time when we didn’t know that dust mites could trigger an allergic response,” Madden says. “And, there might be other insects we don’t know we have an allergic response to. On the flip side, there might be insects in our homes that provide some help by eating fungal spores we don’t want to live with. We’ll only know this if we do further research.”

Understanding the arthropods that live with us is an important step toward further researching their significance to our health. For instance, there is evidence that a biodiverse environment can actually desensitize us from allergies if we are exposed to many microbes at a young age.

“Timing is everything,” points out Ronald Purcell, M.D., an allergist at the Cleveland Clinic. “Studies suggest that if you are exposed to allergens, bacteria and molds before 12 months of age, the exposure might help protect you — and that makes sense because that first year of life, your immune system is learning friend vs. foe, whether that’s airborne allergies or food.”

We know that dust mites do cause some people to itch, sneeze and rub their watery eyes. “The biggest worry is uncontrolled asthma,” Purcell says, relating that most patients who come in with allergic symptoms don’t point a finger at dust mites or cockroaches. Skin testing reveals the culprits.

The presence of dust mites in humid environments, which was mapped in the study, is not surprising. “Dust mites get their water from the air, and it turns out they are 75 percent water,” Purcell says.

As for the arthropods found in the study, Purcell suspects that “most of the critters don’t seem to be a real interest from an allergy standpoint.”

PMPs who know a client has an allergy to dust mites or cockroaches might recommend a visit to an allergist, who can offer some pointers for creating a less appealing environment. For example, Purcell suggests encasements for pillows, mattresses and box springs. Wash them in hot water (120°F to 130°F) twice a month and use the hot dryer setting to kill dust mites and remove allergens. Forget the air filter. “Dust mites don’t get into the air that much,” Purcell says.

While dust mites can have a negative health relationship with humans, Madden acknowledges, most of the insects identified in the study do not. And, customers shouldn’t assume that sharing our homes with hundreds of arthropods makes our spaces contaminated or dangerous. That’s just not the case.

Instead, the research reveals intricate food webs and fascinating microbiological relationships that make homes as ecologically rich as, perhaps, the great outdoors. Madden says, “This is a different way of looking at insects and a story that rarely gets told.”

The author is a frequent contributor to PCT.