Pollinator of the Week: Virescent Green Metallic Bee

A female virescent green metallic bee. Image from United States Geological Survey Bee Inventory and Monitoring Lab.

This entry is from Lucas Costner, an undergraduate horticulture student at Oregon State University. It highlights a common Oregon pollinator.

While there are approximately 4,000 species of native bees in the United States (an estimated 500 of which call Oregon home), I’ve decidedly landed on one as my very favorite (1, 2). This flying iridescent blue-green gem, covered in golden hairs, and sporting a pitch black abdomen with white or yellow bands is Agapostemon virescens, the virescent green metallic bee. Found throughout the United States and southern Canada, these members of the sweat bee family (Halictidae) are common and beautiful (3).

As with other species of the genus Agapostemon, the virescent green metallic bee is a communal soil nester (3). These nests are composed of underground tunnel systems, marked by a main vertical burrow that branches off into several larger nesting areas complete with horizontally running tunnels and cells (4). In these cells, female bees leave a gift of pollen and nectar for a single egg before filling the tunnel with an insulating layer of soil (4). Soon a babe is hatched and, after eating and growing, the mature offspring dig their way out to start foraging!

Virescent green metallic bees are polylectic, meaning they collect pollen from a wide variety of floral resources (4). This is lucky for us gardeners, because we can plant from over a dozen common flower genera and provide the bees with forage. This point is underscored by a 2014 study that sampled bee species in Chicago, finding that the virescent green metallic bee was one of the most common species in the city (5). The same study noted that in more densely populated neighborhoods, the overall composition of bees shifted to more heavily consist of  bees like the virescent green metallic bee and the European honey bee (5). As our cities continue to grow and the needs of urban communities become more pressing, this is good news for the virescent green metallic bee and other generalist pollinator species that can benefit from a relatively wide selection of floral resources.

A virescent green metallic bee emerging from a nest. Image from the University of Maine Cooperative Extension.

Having met the virescent green metallic bee for the first time this past summer working with Aaron Anderson on his native plants study at the North Willamette Research and Extension Center, I was curious to see which plants selected for the study had been previously identified as providing forage for the bee. From our list, the common sunflower (Helianthus annuus), yarrow (Achillea millefolium), showy milkweed (Asclepias speciosa), Douglas aster, (Symphyotrichum subspicatus), common camas (Camassia leichtlinii), wild strawberry (Fragraria vesca), Oregon iris (Iris tenax), sedum (Sedum oregonense), and goldenrod (Solidago canadensis) all make the cut (3).

Flowers are important for these bees for more than just food, however; as they also provide a rather scenic backdrop for the crucial business of mating. While female bees will return to the nest after emerging from the incubator cells in the spring, the male bees spend their days foraging, mating, and sleeping out in the cold, eventually dying at the end of the season (4). The females are the real beneficiaries of the underground nests, returning here to hibernate and lay their own eggs, and sharing in the joint responsibilities of guarding and maintaining the tunnels (4).

My favorite green bee may be relatively abundant and may not require as much help as other species in the way of specific planting regimes, but (as with all native ground nesting bees) leaving some undisturbed open space in your yard or garden can go along way to provide habitat. According to the Xerxes Society, nearly 70% of all native bees are ground nesters (6). To offer nesting habitat in your garden, simply leaving a couple feet of well-drained, bare or sparsely vegetated soil available in a sunny location will do (1, 6). The bees will take care of the rest — hopefully you will have the opportunity to enjoy them in your own garden next summer!

Sources:

1. Moisset, Beatriz, and Stephen Buchmann. “Bee Basics: An Introduction to Our Native Bees.” USDA Forest Service, Mar. 2011.
2. “Oregon Native Bee Atlas.” Oregon Bee Project, blogs.oregonstate.edu/beeproject/bee-atlas/.
3. “Agapostemon virescens.” Discover Life, 9 Nov. 2017, www.discoverlife.org/mp/20q?search=Agapostemon%2Bvirescens.
4. Abrams, Judith, and George C. Eickwort. “Nest switching and guarding by the communal sweat beeAgapostemon virescens (Hymenoptera, Halictidae).” Insectes Sociaux, vol. 28, no. 2, 1981, pp. 105–116., doi:10.1007/bf02223699.
5. Lowenstein, David M., et al. “Humans, bees, and pollination services in the city: the case of Chicago, IL (USA).” Biodiversity and Conservation, vol. 23, no. 11, Oct. 2014, pp. 2857–2874., doi:10.1007/s10531-014-0752-0.
6. Shepherd, Matthew. “Nests for Native Bees.” The Xerxes Society for Invertebrate Conservation, 2012.