We’ve all been outside drinking a pop at a picnic, when these little black-and-yellow creatures start flitting around and trying to get into the drink.
“Sweat bees,” someone will say, shaking his or her head. “They’re so annoying.”
Learning about bees as we put together the bee identification spinner for the new Pollinator Paradise addition, what are called sweat bees didn’t match up with what I’ve called sweat bees before.
Doing a little more looking, what Iowans often deem sweat bees can actually be hover flies, which mimic bees through their coloring but are actually harmless flies, or sometimes more aggressive yellowjackets, which are also not bees but wasps. (Read about that here.)
Real sweat bees are in the family Halictidae and predominantly aren’t even black and yellow!
Metallic green sweat bees
Let’s start with metallic green sweat bees. These are found in the genuses Augochloropsis, Augochlorella, Augochlora and Agapostemon. Dependent on the species, these native bees may be all green, may have highlights of reddish-yellow and could even have a green head and thorax with a striped abdomen. A striped abdomen might be black and yellow, but it can also be black and white.
These bees are ground nesters — except for Augochlora, which nest in rotting wood — and great pollinators, collecting pollen on their hind femurs and tibia. They are generalist pollinators, which means they will forage on a variety of plants instead of a certain species. However, Agapostemon species do seem to like plants in the aster family in the summer and autumn. Augochloropsis also visit crops such as tomatoes, potatoes, eggplant and peppers. These flower require buzz pollination, and these bees have the ability to sonicate and release pollen from these flowers.
There are approximately 15 species of Agapostemon in the U.S. and Canada, three species of Augochloropsis, seven species of Augochlorella and six species of Augochlora.
The term “sweat bee” came about originally from insects that fly around after sweaty people outdoors, trying to land on human skin to feed on sweat for salt and minerals. Bees in the genus Halictus do just that. These are true sweat bees, drawn to human sweat.
Halictus are small bees, about 7-13 mm in length.
They can bee solitary, communal or social, having been found to have social ground nests in warmer climates and solitary nests in cool climates.
These sweat bees are also generalist foragers, visiting a wide array of flowers throughout the summer months. They often like open flowers where pollen and nectar are easy to access, such as coneflowers, butterfly milkweed, goldenrod and asters.
There are approximately 10 species of Halictus in the U.S. and Canada.
This is a huge genus of native bees, with almost 300 species in the U.S. and Canada. They are considered small sweat bees, ranging in size from a tiny 3 mm to 10 mm.
Because there are so many species, the behaviors within this genus also vary. These small sweat bees can be solitary, primitively social or even social parasites — meaning they invade nests and become the dominant egg-layer. They nest in the ground or in rotting wood, such as dead trees or logs lying on the ground. They also forage on a variety of plant species, from bloodroot and wild geranium to boneset, golden Alexanders and goldenrod.
Like in the Apidae family, the Halictidae family also has some annoying relatives — cuckoo bees.
Being cuckoo bees means that these bees do not have their own nests, instead laying their eggs in the nests of other bees. The Sphecodes female goes into the brood cell of another bee, destroys the host bee egg or larva and lays her own egg. The rest of the time, the adult bees forage for nectar, but they do not have any pollen-collecting structures.