Introduced to help pollinate crops, the non-native bee Anthophora villosula is now finding its own way in the U.S., present in several mid-Atlantic states. Researchers are now evaluating its range and potential impact on native bee species and ecosystems, though as yet it hasn’t earned “invasive” status. (Photo by Shane Windsor via iNaturalist, CC BY-NC 4.0)

By Carolyn Bernhardt

In the 1940s, 5 million managed honey bee colonies buzzed about the United States. Today, that number has nearly halved. Experts cite various factors, including a declining number of farms coupled with increasing opportunities for off-farm jobs, as well as drops in honey prices and the onset of Varroa mites and other bee health issues in the late 1980s.

In response, the U.S. began importing exotic pollinators, selecting certain species based on several factors, such as how well they would adapt to the climate here, how costly they are to manage, and how well they can work alongside native bees. Some of these introduced species have established populations and expanded distribution outside of their managed ranges.

Only a limited supply of research into these introduced species exists today. Still, findings show that some of these introduced species have negative effects on local bee and floral communities. Some introduced species compete with native bees, disrupt plant-pollinator networks, hybridize with native species, and spread diseases.

In an article published in December in Annals of the Entomological Society of Americaby researchers at the USDA Agricultural Research Service Bee Research Laboratory, experts report on the ongoing distribution expansion of one such introduced species of bee, Anthophora villosula. This bee was first introduced into the United States in 1988 by USDA scientists and has managed to establish itself here largely unnoticed, until now.

Getting to Know an Exotic Bee

After joining the USDA-ARS Bee Research Lab as a postdoctoral fellow, Stephania Sandoval-Arango, Ph.D., began studying A. villosula. While a high-quality reference genome was already in the works through Beenome100, Sandoval-Arango still discovered major gaps. “I realized that there was no clear understanding of where A. villosula was distributed and the habitats it was occupying, even though native bee scientists had suggested that it could be invasive and expanding its distribution,” she says.

Native to eastern Asia and known colloquially as the Asian shaggy digger bee, A. villosula has been found in China, Japan, Korea, and Taiwan, as well as in single records from Malaysia and Papua New Guinea. Researchers behind the decision to import the species observed it in its natural habitat and noticed it was a generalist pollinator, pollinating blueberries, strawberries, apples, and beans, and visits many native flowers. These bees were also not aggressive and performed buzz pollination, a key aspect of efficiently pollinating blueberries.

In 1988, the bees arrived from Sugata-Cho, Matsue, Japan, and 56 diapausing bees were reared at the USDA Beneficial Insects Introduction Research Laboratory in Newark, Delaware, and emerged in April 1989. Researchers then tested whether A. villosula could effectively pollinate blueberries in the U.S. They ran five years of trials in screened cages with different blueberry species and other plants. The bees visited the plants, nested in adobe blocks, survived the winter, and were active from early spring to early summer. A later study in Maine compared A. villosula to a common native bumble bee and found both pollinated blueberries equally well. Because A. villosula would be cheaper to use, researchers recommended it for commercial pollination.

However, concerns about bringing exotic bees into the country and their possible impact on native species stopped further field testing and ended the breeding program, leaving only one remaining population at the Beltsville research center. And yet, A. villosula has been increasingly reported outside of its introduction site over the past 35 years.

Introduced to help pollinate crops, the non-native bee Anthophora villosula is now finding its own way in the U.S., present in several mid-Atlantic states. Researchers are now evaluating its range and potential impact on native bee species and ecosystems, though as yet it hasn’t earned “invasive” status. Circles indicate records from human observations on iNaturalist, while triangles indicate specimens preserved in collections. (Image originally published in Sandoval-Arango and Evans, 2025, Annals of the Entomological Society of America)

Measuring Its Impact

Introduced species can become invasive if they establish themselves and spread widely. Researchers have long deliberated on what makes a species “invasive” or “non-native.” Traits that they consider important to a species status as invasive include fast reproduction, strong ability to spread, adaptability to different environments, and being able to eat many types of food.

However, having these traits doesn’t guarantee a species will become invasive. Rather, these factors help scientists evaluate possible impacts on native plants and pollinators when a species is introduced to a new area. Researchers use an impact-based classification system that looks at mechanisms like competition, interactions with other exotic species, hybridization, and disease spread. Based on these factors, an introduced species can be rated as having minimal to massive environmental impact or labeled data-deficient if there isn’t enough information. For the study on A. villosula, the USDA-ARS team looked at whether the species should be considered invasive based on these criteria.

The experts confirmed the bee’s presence in Maryland, the District of Columbia, Virginia, Pennsylvania, North Carolina, and New Jersey. This expanding distribution of A. villosula throughout the mid-Atlantic indicates that the species has been able to establish and survive the harsh conditions of winter without management—a finding that opposes earlier observations. More recent research on the species suggests A. villosula is heterothermic, allowing the bees to warm up quickly and tolerate colder climates. The bee is also highly prevalent in urban settings which, when coupled with its cold tolerance, leaves native bee experts expecting it to continue expanding across eastern North America.

Despite this, the team found insufficient information to classify the species with respect to its impact. But since it’s buzzing around the eastern seaboard, the team says the species warrants attention to understand its potential impacts on native communities, so that its invasive status can be evaluated and management plans proposed. “We have projects looking at the microbiome and population genomics of A. villosula,” Sandoval-Arango says. “We hope to share results from that research soon.” However, she is quick to note that the team does not presently have enough evidence to call the bees invasive. “Until then, we can only say they are introduced or exotic.”

The team also advocates for monitoring programs and community science as a fundamental step to document the real spread of the species in North America, gather information on interspecific interactions, and document behavioral aspects that might impact native bees. Online photo-sharing platforms such as iNaturalist, they say, provide a great opportunity for surveillance of the species through community science.

“I hope that with our article, more native bee scientists will be interested in the species,” says Sandoval-Arango, “and we will generate better data for this bee.”

Carolyn Bernhardt, M.A., is a freelance science writer and editor based in Portland, Oregon. Email: [email protected].