Pollinator of the Month – Striped Sweat Bee

July 27, 2022

Written by Amy Yarger, Butterfly Pavilion Horticulture Director

In popular culture, the universal calling card for bees is bold black and yellow stripes. We associate this striking color combination with bees for a reason – once you get stung, you never forget! Seeing yellow next to black triggers those painful memories and reminds us to give danger a wide berth. But with 4000 species of bees native to the United States and close to 950 in Colorado, you are also bound to see bees sporting entirely different palettes in real life – silvery gray digger bees with mirror-bright eyes, furry bumblebees with bold red stripes. And then there’s the striped sweat bee who takes its look to a whole new level, looking more like jewelry than a hardworking insect.

The striped sweat bee belongs to the sweat bee family, Halictidae, which tend to be small, shiny and less furry than honeybees and bumblebees. Other members of this family are notorious for sipping human perspiration, sometimes giving a tiny sting if disturbed in their salty quest. However, striped sweat bees do no such thing, preferring the sweet stuff instead. These medium-sized (about half an inch long) native bees have metallic green or bluish-green heads and bodies, but their abdomens are often striped. Males sport yellow and black bands, while females have white and black stripes on their abdomens or no stripes at all.

There are over 40 kinds of striped sweat bees found from Canada to Argentina, found in a variety of habitats, including prairies, gardens and foothills. Striped sweat bees are generalists, which means that they visit many kinds of flowering plants. Some of their favorites are relatives of sunflowers, beans and roses. I often see them on different kinds of coneflowers, from black-eyed Susans to purple coneflower, but I also see them on my Apache plumes and cinquefoil bushes. Their scientific name Agapostemon translates to “stamen loving” because these bees are pollen-collectors. They have short tongues and can’t get nectar or pollen from deep flowers with long tubular corollas, so smaller flowers fit them best.

Striped sweat bees are usually solitary in their nesting habits. Each May, a female bee constructs a nest in bare ground or an open streambank. Each nest is made up of a long vertical tunnel with many short lateral tunnels each ending in a single cell. Some of these nesting tunnels reach 5 feet in depth! The female bee then will visit flowers to collect nectar and pollen, sticking her cache to her hind legs for transport. Eventually, she’ll use the nectar and pollen to form nutritious pollen balls, sort of like bug-sized protein bars.  The bee mama places each pollen ball in a separate cell of her nest, then lays a single egg on top of the pollen ball. When the egg hatches, the larva has a complete food source while it grows. Multiple females may dig burrows in the same location, and in some species, females may even share one entrance to multiple nests, like an underground apartment building. This arrangement helps guard against nest parasites. You can sometimes see a bee sticking her head out of the nest hole, keeping watch. Later in the summer, the new adult males and females emerge and mate to continue the generation the following year. Only mated females survive the winter, returning underground to wait until spring.

Striped sweat bees are adaptable foragers and strong fliers. They can fly relatively long distances for such small creatures, looking for habitats with high densities of flowers. Landscapes with large swaths of colorful, blooming plants are their favorite places. If you want to create a space to attract metallic green bees, plant clumps of 7-11 of the same plant together, especially native coneflowers, Apache plume, blanket flower and sulfur flower. Late spring and summer blooming plants with bright colors and shallow shapes are the best for striped sweat bees. You can also help striped sweat bees by encouraging ground nesting – avoid using landscape fabric and keeping wild areas undisturbed. These simple steps make it more likely that the next time you are in your garden, there may be a flying jewel right under your nose!

Want to learn more about pollinators and how to help them? Contact Butterfly Pavilion’s horticulture department at habitat@butterflies.org!