In a study of the abundance “nuisance arthropods”—defined as any arthropods other than cockroaches or bed bugs—in homes, researchers at Rutgers University used sticky traps to sample arthropod abundance in over 1,500 apartments in New Jersey. Flies were the most abundant nuisance arthropod caught, and among flies, the most common (42 percent) were fungus gnats, such as these gnats in the genus Bradysia. (Photo by Whitney Cranshaw, Colorado State University, Bugwood.org)

By John P. Roche, Ph.D.

We’ve all seen them. Flies or beetles or silverfish, flying around the house, crawling in the kitchen, lurking behind a box in a closet. They generally aren’t of medical concern, like the mosquitoes that spread viruses, and they aren’t of significant economic concern, like the termites that can destroy structures. But they can definitely be, well—a nuisance. And sometimes they can present problems such as causing itchy skin, acting as allergens, or contaminating food.

To explore how abundant such “nuisance arthropods” are in homes—and how that measures up against residents’ perceptions of their abundance—researchers at Rutgers University sampled arthropod abundance in over 1,500 apartments for a new study published in June in the Journal of Economic Entomology.

Sabita Ranabhat, a master’s student (left), and Xiaodan Pan, a Ph.D. student (right) at Rutgers University, examine a sticky trap in a study of nuisance arthropods. The study found that, of 1.587 apartments in New Jersey sampled with sticky traps, 42 percent contained nuisance arthropods. Flies were the group most prevalent in the traps, followed in turn by beetles, spiders, ants, booklice, and “other.” (Photo courtesy of Changlu Wang, Ph.D).

The study was led by Changlu Wang, Ph.D., professor and extension specialist in entomology at Rutgers, and colleagues Salehe Abbar, Ph.D., Xiaodan Pan, Sabita Ranabhat, and Richard Cooper, Ph.D. The team defined nuisance arthropods as any arthropods other than cockroaches or bed bugs and studied them by introducing sticky traps—small boxes with a surface of sticky glue—into 1,587 apartments in four cities in New Jersey. They left three sticky traps in each apartment: two in the kitchen and one in the bathroom. After 14 days, they collected the traps and counted what arthropods had been caught. They also conducted 1,020 interviews of apartment residents to ask which arthropods they had seen in their homes. The sampling was done between February 2018 and July 2019.

What they found was intriguing. Forty-two percent of apartments had nuisance arthropods in their traps. The types of arthropods found were, in order of prevalence, flies, beetles, spiders, ants, booklice, and “other.” Of the flies caught, 42 percent were fungus gnats, 18 percent were phorid flies, 17 percent were moth flies, 10 percent were fruit flies, and 8 percent were midges. Arthropods in the “other” category included moths, centipedes, and silverfish. No traps had mosquitoes.

The prevalence of arthropods varied by season, with an average of 72 percent of apartments per building sampled having nuisance arthropods in the summer months, but only an average of 14 percent having nuisance arthropods in the winter months. This difference, which was statistically significant, makes sense: Warmer temperatures in summer months lead to higher reproductive rates of arthropods, leading to higher abundance inside and outside of homes.

In their interviews, the researchers found that just 13 percent of residents said they had seen nuisance arthropods—far under the 42 percent of apartments in which nuisance arthropods were caught in traps. Even more intriguing, of that 13 percent of residents who said they had seen nuisance arthropods, 49 percent of their apartments had no nuisance arthropods in their traps. This means that either insects were seen but did not end up being caught in sticky traps, or the interview-reported sightings were fleeting or even imagined (also known as “delusory infestations”).

Of significance in the study is the confirmation that sticky traps are effective for sampling crawling arthropods and some flying arthropods in homes. “Placing sticky traps in homes is a very good method for monitoring indoor arthropods,” Wang says. Another important finding was that the perception residents had of the presence of insects in residences differed considerably from the actual prevalence of arthropods present as represented by the sticky trap data. Meanwhile, the sticky trap data can help the public understand more about the arthropods in their homes. “People need to be aware that the arthropods revealed from sticky traps are not medically important,” Wang says. “But they can be a nuisance or cause economic loss due to food contamination.”

In terms of practical implications, residents can help control the number of nuisance arthropods by how they maintain their homes. “Water leaks, poor sanitation, cracks and crevices around windows and doors, and old food materials,” Wang says, “can allow these arthropods to develop into large numbers. So, while people should not be scared by these creatures, they can keep their home well maintained to minimize their abundance.”

John P. Roche, Ph.D., is an author, biologist, and scientific writer with a Ph.D. in the biological sciences and a dedication to making rigorous science clear and accessible. He writes books and articles, and provides writing for universities, scientific societies, and publishers. Professional experience includes serving as a scientist and scientific writer at Indiana University, Boston College, and the University of Massachusetts Medical School, and as editor-in-chief of science periodicals at Indiana University and Boston College.