Native Animal Profile: Sweat Bees (aka Halictid Bees)
Maryland is home to 437 species of bees, just over a quarter of which are members of the family Halictidae: sweat bees. Unlike other bee families, like the Andrenids (mining bees), sweat bees are often generalists, visiting whatever flowers pique their interest. While this may seem like an advantage, sweat bees have to navigate different flowers to extract pollen and nectar, while also possessing the ability to metabolize pollen from multiple plant species. Both techniques are no easy feat for small and short-lived insects! Despite their generalist nature, sweat bees are important pollinators for many wildflowers and crops including sunflowers, stone fruits, apples and alfalfa.
As their common name suggests, sweat bees are attracted to perspiration. As we toil in the garden, sweat bees will visit to imbibe our sweat. When swatted, they sometimes will sting, but their venom often only causes mild irritation.
The majority of sweat bees are solitary, with a handful exhibiting some semblance of sociality. Social bees, like European honeybees, live in colonies and have a division of labor, while solitary bees nest alone and have to do everything, from foraging to nest building, themselves. Interestingly enough, species like Halictus rubicundus can switch between solitary and social behaviors. In Great Britain, researchers found that Halictus rubicundus increased social behavior under predicted climate change scenarios. This ability to adapt along with their generalist feeding strategies may be advantageous for this species’ survival as the climate changes.
Sweat bees are made up of both metallic and non-metallic bees. While most are dull to metallic black in color, some of the more common and easy to distinguish sweat bees in Maryland are metallic green or blue. Two species found throughout the state include Agapostemon virescens and Augochlorella aurata. The former species has an iridescent green thorax and a striped black and hairy abdomen. The latter species is metallic green. Both species can be seen actively foraging April through October in Maryland.
As with many of Maryland’s native bee species, most sweat bees nest underground in bare soil that is exposed to the sun. Some species, however, will nest in rotting wood while others are cleptoparasites that lay their eggs in other bee’s nests. To help nesting sweat bees, consider leaving patches of open soil close to flower beds while restricting or eliminating pesticide use. Interestingly enough, research by Cane (2015) found that landscaping pebbles mixed into soil was more attractive to nesting Halictus rubicundus than bare soil alone. Decaying wood can also be used as nesting habitat as well as overwintering habitat for some species. In addition to providing nesting habitat, consider planting a variety of native flowers such as asters and their relatives like goldenrods to help attract varying species of sweat bees.
Buckley, K. C. Z. Nalen, and J. D. Ellis. 2019. Sweat Bees, Halictid Bees, Halictidae (Insecta: Hymenoptera: Halictidae). https://edis.ifas.ufl.edu/in897 Accessed October 2, 2019.
Cane, J. 2015. Landscaping pebbles attract nesting by the native ground-nesting bee Halictus rubicundus. Apidologie. 46 (6): 728–734.
Schürch, R., C. Accleton, and J. Field. 2016. Consequences of a warming climate for social organization in sweat bees. Behav Ecol Sociobiol. 70: 1131–1139.
Fall is my favorite time of year. I love the sights and smells as the summer fades, and it is a great time to be out in the garden. Currently, many animals are in the midst of migration, and we are having some record breaking dragonfly migration swarms this year! As fall unfolds, here are a few things to consider this time of year:
In addition, last year’s rainy summer, coupled with this year’s drought and other factors, have taken a toll on oaks in our region. The University of Maryland Extension has put together an informative and concise article on Why Oak Trees are Declining. If you are in need of trees and shrubs for conservation or lumber, check out the Maryland State Tree Nursery which is accepting orders for Spring 2020.
In this issue, you can learn about a lovely native wildflower, the New England aster, as well as a native group of bees called sweat bees that help to pollinate New England aster and its relatives. In addition, with advances in plant research, we are learning more about how cultivars affect our landscapes. Finally, learn about an up and coming invasive insect in Maryland, the spotted lanternfly, and how to report if you see one in the state.