Sociality
The majority of bee species, approximately 90%, have a solitary nest. The remaining 10% have subsocial, communal, semi-social, or eusocial nests. For example, Bombus (bumble bees) establish annual eusocial colonies, and many sweat bees (family Halictidae) have eusocial, semi-social, or communal nests. The highly eusocial non-native Apis mellifera (European honey bee) produces large perennial colonies that behave like a superorganism with a sophisticated division of labor, communication between foraging bees, and one long-lived queen that performs all of the egg-laying.
Eusocial
There are a number of factors that determine if a particular bee species is considered a eusocial species. These include multiple overlapping generations (queen and her offspring) within a nest at one time, a division of labor with individual roles (tasks) such as nest defense and foraging, and cooperative brood care with offspring helping to rear their siblings. ​The fascinating thing about social nests is the worker females forego mating and reproduction, and instead help rear the offspring of another female. The relatedness of the females within a colony is one reason scientists cite for this dynamic to evolve and be a successful strategy. In Minnesota, bee species in the genera Augochlorella, Bombus, Halictus, and Lasioglossum have social nests.
Semi-Social
A semi-social nest operates similarly to a social nest, but the primary egg laying female is the sister of the other females within the nest. This arrangement can occur in the family Halictidae (sweat bee) nests or in social nests when the queen dies and a daughter takes over as queen, becoming the primary egg-layer. In Minnesota, bee species in the genera Augochloropsis have semi-social nests.
Communal
In communal nests, multiple females share a nest entrance and main burrow, but each female independently constructs and provisions their own brood cells within the nest. These nests frequently occur in aggregations (grouping of many nests) or less often, singly. In Minnesota, bee species in the genera Agapostemon, Augochloropsis, and Lasioglossum have communal nests.
Subsocial
In subsocial nests, females establish and provision nests on their own but interact with their developing larvae as they progressively provision the brood cells. These females may live long enough to interact with their adult offspring.
Solitary
​Solitary nests are those with a single female bee responsible for completing all the tasks carried out by many bees in a social nest: establishing and constructing a nesting site, foraging for provisions and/or nesting materials, laying all the eggs, and defending the nest. Ultimately, the single female has only a short four- to six-week lifespan to complete these tasks. Compared to social nests, many things can go awry in a solitary nest with just one occupant. For example, solitary nests are more susceptible to attacks by predators. Also, if a female perishes before completing her nest provisioning and egg laying, there is no bee ready to take her place. If she is successful, she fully provisions a nest but never interacts with her offspring, typically perishing before her offspring emerge as adults.
No Nest
Cleptoparasitic (cuckoo) bees do not construct their own nests. Instead, they lay their eggs in the nests of other bees, sneaking inside while the host bee is away collecting provisions or nesting materials. Either the cuckoo bee or its larva kills the host egg (or larva) in the brood cell. The cuckoo bee larva then develops by feeding on the provisions provided by the host bee. Learn more about the cuckoo bee genera and their hosts here.
Bombus bimaculatus
(two-spotted bumble bee)
Eusocial Nest
Augochloropsis humeralis (metallic green sweat bee)
Semi-social Nest
Agapostemon virescens (metallic green sweat bee)
Communal Nest
Andrena (mining bee)
Solitary Nest
Coelioxys (cuckoo bee)
No Nest
Life Cycles
Bees and other insects in the order Hymenoptera undergo complete metamorphosis with four distinct development stages: egg, larva, pupa, and adult. The type of bee, their sociality (whether they have solitary nests, form colonies, or something in between), the number of generations produced in a growing season, and the phenology of the adults, determine which development stage they may be in at a given time of year. Most solitary bees are univoltine (producing one generation per year) with a twelve month egg-to-adult life cycle that results in a solitary univoltine species emerging at approximately the same time each year. Social or semi-social bees typically produce one or more generations per year. A bee that produces two generations per year is bivoltine.
Complete Metamorphosis
Egg
During complete metamorphosis, each of the four development stages are unique or distinct. The elongate, white-opaque egg is typically laid on, under, or suspended above the pollen provisions. In general, the size of the egg is dictated by the physical size of the adult female bee and can range in length from 1 to 20 mm (0.04 to 0.79 inches). The female either fertilizes the egg with sperm, producing a female offspring that is diploid (having two sets of chromosomes, one from the mother the other from the father), or foregoes adding sperm, producing a male offspring that is haploid (having one set of chromosomes, the mother's). This sex determination system is referred to as haplodiploidy. After the egg is laid, cell division initiates within the egg, resulting in the development of the first instar larva. With the aid of its lateral spines, the first instar larva tears open the egg chorion (membrane). As it emerges from the egg, the larva sheds its larval skin.
Larva
The egg typically hatches within hours to a day or so. The small second instar larva emerges and begins feeding on the pollen provisions provided in the nest brood cell. The larva is off-white and grub-like in appearance with developed mouthparts for feeding, but lacks eyes, legs, wings, and other anatomical features of a pupa or adult. Larvae "breathe" through spiracles, located on their abdominal segments. While feeding on the provisions over the next one to three weeks, the larva grows in size and molts three more times, passing from the second to the fifth instar stage. It sheds its skin at each molt.
In the fifth instar stage, the larva defecates, either during feeding or after all the provisions are consumed, and ceases feeding. At this pint, it may envelops itself in a silken cocoon (or not). Most solitary bees in Minnesota produce a cocoon, but a few genera do not, for example, Anthophora. Spinnerets in the larva's mouthparts (salivary openings) produce strands of silk to form the cocoon. Once completed, the cocoon becomes a safe enclosure, protecting the larva now in the prepupal stage, from parasites, pathogens, and desiccation. For protection from drying out during the long overwintering period, the larva typically develops a thick cuticle. The majority of solitary bees overwinter in this prepupal stage in a period of suspended development (diapause).
Pupa
Hormonal signals initiate the metamorphosis from larva to pupa within the silken cocoon. During the pupal stage, the larval cells and tissues are completely reorganized to begin developing features of the adult such as a head with antennae, compound eyes, mouthparts, a thorax with six legs, undeveloped wings, and an abdomen.
The pupa develops spines on various parts of the body that help with movement (rotation) and provide support. The pupal stage typically occurs over one to two weeks. When development is complete, after the exoskeleton has hardened and the wings have expanded, the adult bee emerges from the cocoon. The bee exits out the end of a nest cavity or, if belowground, it excavates a vertical emergence tunnel, using its legs and mandibles, to reach the soil surface.
Adult
Other than social, semi-social, or communal reproductive females or queens, adult bees have a relatively short lifespan of two to five weeks. In general, males are alive for two weeks at most, long enough for them to search for and find a female for mating. Females live longer than males and have several key tasks to produce the next generation of bees including establishing a nest, foraging for larval provisions and food for themselves, laying eggs, and defending the nest from natural enemies. Social, semi-social, and communal reproductive females mate at the end of the growing season, overwinter as adults, then live for one to several months after emerging the following spring.
Bombus (Bumble Bee) Annual Social Nest Cycle
New Reproductive Females (Gynes) Overwinter as Adults
Gynes emerge from hibernation.
Gynes establish nest and collect pollen and nectar from flowers.
Males begin emerging.
New gynes emerge from nest and visit flowers to sequester fat.
New gynes excavate a
shallow hibernation burrow.
Males, workers, and queen perish.
NEST ESTABLISHED
Gynes search for a nest site.
Some males
establish
territories.
New gynes mate
with a male.
NEST ENDS
Workers emerge from nest and collect pollen and nectar.
Spring-Emerging Solitary Bee Nest Cycle
One Generation Per Year, Overwinters as a Prepupa
Most solitary bees overwinter as prepupae and are univoltine, producing one generation per year. This graphic illustrates a spring-emerging solitary bee, Andrena ziziae. A similar timeline, repositioned later in the growing season, would illustrate the nest cycle for a summer- or early autumn-emerging solitary bee.
* photos depict cavity-nesting bee
Early Spring-Emerging Solitary Bee Nest Cycle
One Generation Per Year, Overwinters as an Adult
A small minority of solitary bees overwinter as adults. For example, Colletes inaequalis (unequal cellophane bee), a ground-nesting bee species, overwinters as an adult within a nest brood cell. This bee is univoltine (producing one generation per year), and the egg-to-adult timeframe is approximately twelve months. Colletes inaequalis emerges between the end of March and the first or second week of April. To exit the brood cell, adults excavate a vertical emergence tunnel.
* photos depict cavity-nesting bee
Spring-Emerging Solitary Bee Nest Cycle
Two Generations Per Year, Reproductive Female Overwinters as Adult
Augochlora pura, a solitary bee that nests in cavities in rotting wood, produces two generations per year (bivoltine). Reproductive females overwinter as adults.
Explore Bee Families
Citations and Further Reading
Danforth, B. N., Minckley, R. L., & Neff, J. L. (2019). The solitary bees: biology, evolution, conservation. Princeton University Press.
Portman, Z. M., Gardner, J., Lane, I. G., Gerjets, N., Petersen, J. D., Ascher, J. S., ... & Cariveau, D. P. (2023). A checklist of the bees (Hymenoptera: Apoidea) of Minnesota. Zootaxa, 5304(1), 1-95.