Agapostemon virescens: this green metallic sweat bee loves your garden

by Chloé Markovits and Nicholas Dorian

Ask a kid to draw a bee, and they will make it big and fuzzy, with black-and-yellow stripes. But did you know that not all bees look like that? One of the most common bees in eastern North America is slender, shiny, and green!

The bi-colored striped sweat bee (Agapostemon virescens) is a stunning green bee that you can find in your garden all year long. It is so beloved that it’s the official bee of Toronto. It lives mostly in the Midwestern and Northeastern United States (but with sightings from coast to coast). To help you spot one, let’s review its life cycle, flower preferences, and appearance. For a quick guide, reference our A. virescens field ID tips.

A. virescens are active for most of the growing season—typically from mid-May through late October—consisting of two generations of females. In mid-May, mated females emerge from hibernation and build nests underground. They use their natal nest or dig a new hole in sparsely vegetated soils. Mulched garden beds, sandy paths, patchy lawns are suitable nesting habitat.

Agapostemon virescens live in underground communal nests.
Agapostemon virescens live in underground communal nests. Females take turns guarding the nests from unwanted intruders like parasitic flies and cuckoo bees. PC: Nicholas Dorian

Unlike the social societies of honey bees or bumble bees, Agapostemon nest in communal societies of egalitarian females. Like apartment complexes in the human world, many females (up to 30!) will live in a single nest, but each will take care of her own offspring independently. A nest has one entrance (a hole at the surface of the ground) which is used by multiple females.

Ground-nesting bees are at risk from predators that aim to steal the nest contents. But Agapostemon has figured out a defense strategy: while some females are out foraging, at least one always stays back to guard the nest. Females take turns guarding the nest, and the presence of a guard reduces the chance of a visit from an unwanted intruder.

While out foraging, A. virescens females gather pollen and nectar. Females can be found on a wide variety of plants—from roses, to strawberries, to sunflowers—but in general have a penchant for plants in the Asteraceae family. In particular, summer-active females love collecting pollen from purple coneflower (Echinacea purpurea), cup-plant (Silphium perfoliatum), false sunflower (Heliopsis helianthoides), and lance-leaf coreopsis (Coreopsis lanceolata).

Agapostemon virescens loves asters like cup-plant.
Agapostemon virescens loves asters! Cup-plant (Silphium perfoliatum) is one of their favorite plants. PC: Nicholas Dorian

In late-July to early-August, a second generation of A. virescens emerges. This generation consists of both males and females. Males cloud around flowers waiting for the chance to mate. They are not welcome back in their natal nests, so males find places to sleep outside. Sometimes, males will sleep together in aggregate in sheltered nooks and crannies– bee slumber parties!

Fall-active females sip nectar from flowers in order to survive winter, but do not build nests or lay eggs. Look for fall-active A. virescens on asters like New England aster (Symphyotrichum novae-angliae), goldenrods (Solidago spp.), and sneezeweed (Helenium autumnale). When temperatures drop, mated females enter hibernation in their natal nests until spring, and males die.

A. virescens females can be easily identified on flowers or with photographs taken with a phone camera. Look for a metallic green thorax and black-and-white striped abdomen.  Males are trickier to distinguish from males of other Agapostemon species but can be identified by their metallic green thorax, black-and-yellow abdomen, and the lack of dark streak on their hind femur.

Agapostemon virescens females can be easily identified via the combination of a metallic green thorax and a black-and-white abdomen.
Female Agapostemon virescens can be easily identified via the combination of a metallic green thorax and a black-and-white abdomen. PC: Nicholas Dorian

If you’re lucky enough to spot one, take a moment to appreciate its fascinating life cycle. Is a male darting around in search of a mate? Or a female working hard to collect pollen for her offspring? Is she hovering close to the ground? That might mean you’ve found her nest! Despite its abundance, there is still much to be learned about this bee. What soils do they like for nesting? How far do they forage? How long do females live after provisioning nests in early summer? Why do females prefer aster pollen over all others? TPI scientists are hard at work addressing some of these questions.

Pollinator Week BINGO!

Every year, a week in June is dedicated to celebrating pollinators. All week long TPI will be posting pollinator-related videos, blog posts, etc. PLUS, you can play BINGO for a chance to win a prize!

To play Pollinator Week BINGO, which features flower-visiting insects you can find in the Northeastern USA this time of year, download and print the Bingo card (below) or screen shot the image on your phone. Take your card/phone outside and if you find the correct insect, mark it off on your printed card with a pen/pencil or with your phone’s photo annotation option.

If you get BINGO! (five in a row, vertical, horizontal, or diagonal, TPI logo is a free space), send a photo of your annotated card to tuftspollinators@gmail.com or tweet a photo and tag @PollinateTufts by 11:59 pm on Friday, June 26. Each completed BINGO! card will be entered in a drawing to win TPI swag and a voucher for a free pollinator-friendly plant at next spring’s TPI plant sale! Limit one entry per person.

For help identifying the insects you observe, download our identification guides or reach out to us with photos via email or Twitter!


Stay tuned for more #PollinatorWeek fun!

Happy World Bee Day!

Did you know there are 20,000 species of bees in the world? And that 4,000 of those species are native to North America? In celebration of World Bee Day, we highlight some of the bees TPI members have studied across the United States and in Costa Rica.

Common eastern bumble bees (Bombus impatiens) are important pollinators of greenhouse tomatoes, blueberries, and pumpkins.
Photo: Genevieve Pugesek

Though the common eastern bumble bee is one of the more common bee species in the Northeastern US (as its name suggests), we still have a lot to learn! With help from Tufts undergrad and grad students, I am working to understand where queen eastern bumble beeshibernate. As it turns out, unlike most other species of bumble bees, these queen bees hibernate right next to the nest they were born in. So, if you are creating habitat for nesting bumble bees, you might be creating habitat for hibernating queens too! If you visit our pollinator gardens (while practicing safe social distancing) this spring, you’re likely to see these fuzzy bumble bees flying around.

Genevieve Pugesek, PhD Student, Tufts University

Yellow-faced bumble bees (Bombus vosnesenskii) pollinate many wild plants as well as crop plants such as tomatoes and berries.
Photos: Elizabeth Crone, Rachael Bonoan

For the past 5 years, I worked on this species in collaboration with Neal Williams (Assoc. Professor, University of California), Rosemary Malfi (now post-doc, UMass Amherst) and Natalie Kerr (now post-doc, Duke University).  We found that yellow-faced bumble bee colonies especially need resources to forage on during early stages of colony development.  In the same way that early childhood nutrition affects human health throughout their lives, early spring flowers help these bumble bee colonies grow!  Spring resources allow colonies to produce larger worker bees that are better at foraging for resources, leading to higher resource return even after the spring pulse of flowers ends.  The importance of spring resources has implications for bee conservation because native plants in California mostly flower during the wet spring, whereas irrigated crop plants mostly flower in the dry summer.  If we want yellow-faced bumble bees to be around to pollinate summer crops, we need to keep spring flowers on the landscape.

Elizabeth Crone, Professor, Tufts University

Hibiscus bees (Ptilothrix bombiformis) pollinate plants in the Malvaceae family including cotton, hibiscus, and saltmarsh mallow.
Photo: Judy Gallagher, Flickr

I spent a summer surveying native bees along Virginia’s Eastern Shore and studying the effects of sea level rise on native bee communities. The hibiscus bee was the most common species found on farms, meadows, and salt marshes along the coast. On steamy summer mornings, this bumble bee doppelganger could be found buzzing around marsh hibiscus or visiting blooming cotton fields.

Jessie Thuma, PhD Student, Tufts University

Blueberry cellophane bees (Colletes validus) are specialists that pollinate blueberries.
Photo: Max McCarthy

Different bee species have different diets; some collect pollen from a wide variety of flowers (generalists) while other species forage on the flowers of only a few types of plants (specialists). I sampled pollen from blueberry cellophane bees to understand what types of floral resources this species uses throughout its flight season in May and June. After identifying pollen samples under a microscope, I found that, true to their name, these bees rarely collect pollen from plants other than blueberry bushes.

Max McCarthy, Undergraduate, Tufts University

Honey bees (Apis mellifera) are generalist forages known to pollinate our crops.
Photo: Rachael Bonoan

I study how honey bees regulate in-hive temperatures in order to protect temperature-sensitive eggs and larvae. In order to develop properly, honey bee larvae must be kept at 32 – 36 °C (about 89 – 96°F). With the help of NSF REU students, I found that when an area of a honey bee hive is exposed to heat stress, the queen stops laying eggs in the “too hot” area. Instead of raising young in this hot spot, worker bees store nectar (food!).

Isaac Weinberg, PhD Student, Tufts University

Squash bees (Peponapis pruinosa) are known for pollinating…you guessed it…squash.
Photo: USDA ARS, Wikimedia Commons

As a lead field technician at UW-Madison, I worked with a team to investigate how the diversity and abundance of floral vegetation on small-scale organic farms impacted bee communities and crop flower visitation. We were interested in cucurbit (e.g. cucumbers, watermelons, squashes) pollination, as these crops rely solely on insect pollination. While I was fortunate to study a diversity of bees in this project, my heart was captured by Peponapis as the males scurried around giant squash flowers. Fun fact: When the squash flowers close mid-day, squash bee males nestle up and sleep in the protection of the closed flower until they reopen the following day. 

Sylvie Finn, Incoming PhD Student, Tufts University

Yarrow’s fork-tongue bee (Caupolicana yarrowi) pollinates wild nightshade, and is parasitized by a cuckoo beeTriepeolus grandis.
Photo: Nick Dorian

Yarrow’s fork-tongue is a large, ground-nesting solitary bee that inhabits high deserts of southwestern US and Mexico. Unlike most bees, it cannot be found during the day, but instead is active pre-dawn and post-dusk. In August 2018, several participants of the 2018 Bee Course and I woke up extra early to find nesting females. We found three nests and carefully excavated the long, sinuous tunnels to claim our prize: brood cells. Most cells contained just a Yarrow’s fork-tongue larva feeding on a slurry of pollen and nectar. In one cell, however, we also found an intruder: the larva of a cuckoo bee (Triepeolus grandis). With formidable mandibles, the cuckoo bee larva kills the host and develops on the stolen provisions. This may sound malicious, but it’s simply how the cuckoo bee lives. About 15% of all bees are cuckoos, meaning these pollinators would cease to exist without their host bees!

Nick Dorian, PhD Student, Tufts University

Stingless bees (Trigona spp.) are generalist tropical pollinators that forage on flowers and meat.
Photo: Rachael Bonoan

This past January, some TPI members traveled to Costa Rica with Tufts University’s Tropical Ecology and Conservation course. There, Nick and I studied mineral preferences of facultative “vulture bees,” stingless bees that forage at meat as well as flowers. We identified five species of bees (including Trigona silvestriana, pictured above) foraging at our baits and found that compared with unaltered baits (i.e. raw chicken), stingless bees tended to avoid baits soaked in calcium and potassium. In contrast, bees visited sodium-soaked baits just as often as unaltered baits. This suggests that like many herbivores, meat-foraging bees are likely limited by sodium and will suck up the salt wherever they can find it!

Rachael Bonoan, post-doctoral researcher, Tufts University

Orchid bees (Euglossa spp.) are known for pollinating orchids in the tropics.
Photo: Atticus Murphy

Can you see the thin yellow object on the back of this shiny green orchid bee? This is a pollinium, a packet of pollen grains, likely from an orchid. Male orchid bees forage at flowers for nectar, which provides nutritional energy, and floral scents, which are used to court females. In Costa Rica, my research partner and I captured orchid bees and used tiny glass tubes to suck up the contents of the crop, where collected nectar is stored. We measured sugar content of the bee-collected nectar and found that bees caught in human-dominated open spaces had more dilute crop contents than those caught in the forest. This may be because the open spaces were sunnier and hotter, driving the bees to drink more water.

Atticus Murphy, PhD Student, Tufts University

Interested in learning more about the bees in your backyard? Check out our insect identification guides! For even more bees, our favorite books are The Bees in your Backyard by Joseph S. Wilson and Olivia Messinger Carrill and Bees: An Identification and Native Plant Forage Guide by Heather Holm.
TPI members at work!