Metallic Green Bees – Genus Agapostemon

Have you noticed any interesting insects recently? It seems like we discover new insect visitors every time we look in Mother Nature’s Backyard. Right now our Plant of the Month (Sweet-scent – Pluchea odorata) is attracting a number of interesting insects (see above).

Late summer and early fall can be a good time to observe insects, depending upon the weather and the types of plants that are blooming. Some insects hatch in the summer and are active now; others are completing their life cycle in early fall. And all can provide hours of interesting viewing. One of the more interesting insect groups – and among the more showy – are the Metallic Green Bees in the genus Agapostemon. These are true native bees in the family Halictidae (the Sweat Bees). But they are quite different from the familiar – but non-native - European Honey Bees.

Metallic Green Bees are found in North and South America. There are about 40 species, with the greatest abundance in temperate regions and Southwestern United States. The Agapostemon are floral generalists, which means that they visit a number of different flower species. Despite their lack of specificity, generalists like Metallic Green Bees can be important pollinators in gardens and in the wild.

Metallic Green Bees are short-tongued, so they favor flowers with a relatively open architecture and easily accessible nectar, which serves as food for adults. Like all foraging insects, they appreciate the convenience of plants with many small flowers clustered together. This in part explains why you’ll notice Metallic Green Bees visiting plants in the Sunflower family (Asteraceae; including Sweet-scent) and the Buckwheats (genus Eriogonum). Both of these plant groups feature many small simple flowers that produce high-quality nectar.

You’ll recognize Metallic Green Bees by their unique coloration. Our local females are often metallic green all over while the males have a yellow-and-black striped abdomen (the rear segment of the body) and metallic green head and thorax (see photo above). They are medium sized bees (about 0.3 to 0.6 inches long) somewhat smaller and slenderer than European Honey Bees. You’re likely to see the females busily visiting flowers, collecting pollen on the brushy hairs of their hind legs. The males will be seen nectaring (sipping nectar) or slowly cruising flowers in search of females.

Most species of Agapostemon are solitary ground nesting bees, although individual bees may nest in close proximity. They build deep vertical nests in the ground or in earthen banks. Metallic Green Bees have two generations per year: the summer generation which is almost all female and the fall-spring generation which includes both males and females. Fertilized females from the fall-spring generation over-winter from late fall until early spring. These females accumulate a layer of fall fat that allows them to survive the winter (note: cold weather kills the fall-spring males, which do not have the fat layer).

Fall-spring females from the previous year emerge in early spring and lay eggs in cells in the underground nests. They provide each cell with a pollen ball to feed the developing larva. The early spring-laid eggs give rise to the summer generation, which is mostly female. The summer generation, which emerges and nests in summer, lays eggs that produce the fall-spring generation. Surprisingly, the fertilized eggs laid by the summer generation give rise to fall-spring females while the unfertilized eggs develop into fall-spring males. The fall-spring generation emerges in fall and includes both males and females. And so the cycle continues, from one year to the next.

The warm days of fall provide a wonderful time to get out and enjoy the out-of- doors. So get out in your garden – or in the wilds - and look for these interesting native bees.