Beyond Honey Bees: The Secret Lives of Solitary Bees
There are over 20,000 species of bees worldwide, with a species breakdown of approximately 250 bumblebees, 500-600 stingless bees, and a mere 8 honey bees. The remaining 19,000 or so bee species are solitary (well, sort of)!
Identifying and differentiating these native pollinators can be a dauting task! Sometimes, classifying specific taxonomic features necessitates examination under a microscope—unless you're a seasoned bee biologist who has spent countless hours distinguishing miniscule wing differences between species. Accurately identifying a bee is essential for understanding its role within its ecosystem, which includes social organization, nesting behaviors, and foraging preferences.
Common Identifying Features: From an Ecological Perspective
While biology encompasses the structure and function of living beings, ecology takes it a step further and focuses on the relationship of a species to its environment, often because of its biological features. Bees are ecologically grouped by variation using three main traits: social organization, nesting behavior, and floral preference.
Social Organization
Bee societies range across a spectrum from solitary at one extreme to highly eusocial at the other. Between these extremes lie communal, quasisocial, semisocial, subsocial, and primitively eusocial behaviors. The 19,000 solitary bees mentioned above have bees in nearly all of these social distinctions (besides highly eusocial), which as you will see can be quite a bit more nuanced than the term “solitary” may suggest.
Solitary bee life is the most prevalent social structure among bees and all other social structures subsequently described are the exception! A solitary female bee constructs her nest (using various locations and materials), fills it with pollen and nectar, and lays eggs in separate cells within the nest. After sealing the egg cells, she dies without ever meeting her offspring. When the offspring hatch, they all leave their original home to go build their own nest elsewhere.
Mining bees are a common solitary bee, however, as described later they will sometimes live in “nest aggregations.”
Communal bees represent a step up from solitary bees, akin to living in an apartment complex. In the case of communal bees, there are many females and each maintains her own unit separate from others. Besides sharing a common entrance, each female behaves much like any solitary bee, constructing and provisioning until her life ends, never meeting her offspring. Occasionally, a communal bee may decide to leave the apartment and live permanently as a solitary bee, blurring the distinction between these two types of social existence.
Metallic green or blue sweat bees can be communal, however, there are other species of sweat bees that are closer to eusocial.
Quasisocial bees present a nuanced social structure that can be challenging to distinguish from others. After the mother passes away, multiple sisters hatch and initially share a nest, similar to solitary and communal bees. Shortly after emergence, one female establishes dominance and assumes control of brood cell construction, so she can subsequently start laying eggs. The other sisters assist in nest building and foraging during a brief period of cooperation. Eventually, each sister departs from the dominant female to establish her own nest. This strategy ensures that at least one nest starts off strong in spring, with later nests having reduced chances of success.
Semisocial bees exhibit an early stage of division of labor. Within the nest, sisters are divided into egg layers and foragers, collaborating to care for the brood. These roles are flexible, enabling colonies to sometimes transition into quasisocial patterns. Also similar to other quasisocial groups, many females may eventually depart to establish their own nests.
Subsocial bees have one female who nurtures her brood and raises her offspring. She feeds, protects, and provides for them until they are fully functioning adults. But instead of hanging around home and helping the nest, each newly emerged female goes out into the world and builds a nest of her own. These bees are close to primitively eusocial bees, since for a short time more than one generation inhabits a nest.
Carpenter bees are often subsocial but can also be closer to solitary in the spectrum.
Primitively eusocial bees begin with a queen that establishes a nest independently. Typically, this involves constructing a wax structure in a protected area and provisioning it with nectar and/or pollen. After laying her initial eggs, the queen resumes nest building. Once her first daughters hatch, they assume responsibility for foraging and caring for the brood, allowing the queen to concentrate solely on egg laying. These colonies persist for just one season and do not survive the winter. It is possible for daughters to go out on their own and start their own nests, which creates an overlap with the subsocial structure. At least one new queen (likely many more) from a colony undergoes a period of hibernation during winter and survives until spring to initiate the cycle anew.
Bumble bees are the common primitively eusocial bee.
Eusocial bees, such as honey bees, are what most people typically associate with bee social structures (despite being the rarest social structure!). These bees live in colonies characterized by a cooperative, hive-minded mentality and are often referred to as a "superorganism." Unlike solitary bees, eusocial bees form perennial colonies capable of overwintering. Within these colonies, multiple generations coexist, working together to gather food and maintain the nest. There is a distinct division of labor with a dedicated egg-laying queen and specialized worker bees responsible for foraging and nest construction. It's worth noting that there are no native eusocial bees in the United States. Honey bees, originally brought over from Europe in the 17th century, are the most common bees kept by beekeepers. They can be found in the wild, however, it is rare for feral honey bee colonies to do well on their own.
Lastly, there are also parasitic bees (Cuckoo Bees)! They do not construct their own nests or forage for their young. They simply lay their eggs in other bees’ nests and let the mother(s) of the nest provide resources for their young. While this may seem like a bad thing, it actually isn’t! High populations of Cuckoo Bees can indicate robust populations of the bees whose nests they usurp.
Cuckoo bees have a unique look, they are black and white and have a very pointy abdomen.
Side note: You might have noticed that male bees were not mentioned in any of these social structures! Typically, male bees follow a straightforward pattern: they emerge only during a specific season, seek out female bees to mate with, and then perish. This entire lifecycle usually spans just 4-6 weeks from their emergence, during which time male bees do no work and consume food stores.
Nesting
All bee species build nests in a variety of places using an array of materials. There are five prominent nesting styles among bees: ground nesters, wood and pith nesters, architects, cavity nesters, and renters.
More than 70% of native bee species are ground nesters, utilizing soil as their primary material for nest construction. Different species have specific preferences for soil texture and composition, ranging from well-drained sandy soils to compacted wet soils. Ground nest tunnels can range in depth from a few inches to as deep as 10 feet! Occasionally, ground nesting bees will dig near each other, forming separate nests in a "nest aggregation."
This is a nest aggregation—each hole houses one solitary female bee. The underground tunnels are in no way connected to each other.
Wood Bees construct their nests in solid wood, pithy stems, and similar reed-like materials. Unlike bees capable of secreting wax, these wood-nesters act as architects, blending surrounding wooden materials with their saliva for nest construction. Some stems are naturally hollow when dried out (known as pithy stems), while others require the bees to use their mandibles to excavate a central tunnel inside the stem. Within this tunnel or carved-out wooden nest, female bees create multiple small compartments, each containing provisions and typically housing between one and ten eggs. A great way to support native wood nesting bees is by building bees hotels! The massive bee hotel below is located at the J.C. Raulston Arboretum!
Known for their intricate construction techniques, architect bees often use unconventional materials for nesting. Architect bees are skilled builders, creating standalone nests from mud, resins, stones mixed with resin, plant fibers, and even animal fur. These materials are blended with saliva to form partitions or cells within their nests, much like wood-nesting bees. Leafcutter bees, depicted in the photos below, demonstrate their unique method of delicately rolling plant leaves into cylindrical shapes to fit in pithy stems or bee hotels. They exclusively work with plant leaves, relying on finding pithy stems as a robust framework to build their leaf nests (they cannot chew wood as wood bees do).
Cavity-nesting bees utilize pre-existing holes or cavities in natural or man-made structures for nesting. They may nest in old underground tunnels, hollowed out trees, abandoned burrows, or even in building crevices. Cavity-nesting bees may modify the cavity to suit their needs, constructing cells (most often out of wax) and provisioning them with pollen and nectar before laying eggs. Honey bees are actually considered to be cavity nesters, since their natural inclination would be to build their nest in a sheltered tree or man-made structure.
This is a bumble bee nest! They like to build nests in locations that are nestled safely away from the elements; often in grasses, shallow holes in the ground, or man-made structures.
Renters are a specialized group of bees that do not construct their own nests but instead take advantage of nests built by other bees or insects. They may parasitize the nests of other bees by laying their eggs in existing brood cells or taking over the entire nest after the original occupants have left. Sometimes they don’t even take care of their own young at all! Cuckoo bees are the common bee renters.
Floral Preferences
Nectar serves as the main carbohydrate source for bees. While most bee species are not highly selective about their nectar sources, their access may be influenced by factors such as body size, tongue length, or seasonal availability. Pollen, is the primary protein source for bees, crucial during their developmental stages and into early adulthood. Both nectar and pollen are essential staples in the diets of all bee species. Seasonally, nectar availability peaks in spring and summer when plants are actively producing it, whereas it tends to diminish in fall and winter. In North Carolina, pollen sources for bees are generally available year-round, except during a couple of the coldest winter months.
Most bees are considered generalists, meaning they adaptably visit a wide variety of flowers for nectar and pollen. In contrast, some bee species are specialists, relying on a specific flowering plant or a narrow range of plants for their food sources. This specialized lifestyle can be challenging, particularly in the face of habitat loss and environmental changes. Evolutionarily, being a generalist tends to be advantageous because it increases the likelihood of finding food sources across different environments. Through the process of cultivating and supporting specific plants, human intervention can sometimes help specialist bees (one may argue that humans are also taking advantage and perpetuating monocropping agriculture practices).
Certain bee species possess a unique ability known as buzz pollination. This involves landing on flowers and vibrating their wings rapidly (at a louder and faster frequency than during flight) to release pollen grains. Approximately 8% of flowering species worldwide depend on buzz pollination as their primary method of pollination. These plants usually have a more unique anther that holds onto the pollen more tightly than most flowering species. Bumble bees and carpenter bees are the common buzz pollinators. The video below shows the process of buzz pollination.
A Quick Note on Importance
The best way to learn about and support native bees is by planting a pollinator garden filled with native flowering plants. In addition to providing forage sources for native bees, it is important to remember that many bees rely on stems, leaves, and soil for nesting. Native bees benefit from non-landscaped natural areas (including untidy gardens!) where specific materials provide essential nesting habitats. Leaving areas of exposed ground or old stems in the garden can serve as nesting sites for native bees and attract a diversity of pollinators to your area. Avoiding chemical pesticides and herbicides can improve the overall health and success of bee populations (not to mention all other ecosystem members).
Native bees are vital for ecosystems, biodiversity, and agriculture. Honey bees excel as generalist pollinators (particularly in agriculture), and often overshadow the crucial pollination efforts of native bees. To learn about Buddha Bee Apiary’s response to this ongoing challenge, check out our blog Re-visiting Our Impact on Native Pollinators.
This video provides all you could ever want to know and more about the native bees of North Carolina: