Of all the native bees in our gardens, the bumble bees are perhaps the most easily recognized, cute and appealing (besides our own adorable honey bees, of course, which are not native to the Americas) with their fuzzy, plump bodies and what we think of as their “typical” yellow-and-black coloration. However, as you observe more closely, you’ll notice many touches of red, orange, pink, white, and gray on various species you’ll find in your garden.

The genus of bumble bees is Bombus, which is part of the same family Apidae to which honey bees, stingless bees, carpenter bees, cuckoo bees, among many others belong: all distant “cousins,” so to speak. Bumbles are quite mellow and nonaggressive.

On very rare occasions one might use its barbless stinger if it were inadvertently stepped on by a shoeless foot, or if it were accidentally trapped in a person’s clothing–or once in a great while, if a nest were rudely and destructively disturbed, calling for defense by the colony. 

Otherwise, bumbles just go calmly about their foraging business.

We have 23 bumble bee species indigenous to Washington and a few more that have entered from neighboring states. There are 50 species resident across the US, and 250 in total that live mostly in the northern hemisphere and higher altitudes around the globe. 

In our Puget Sound area of the Pacific Northwest, the most common species we see are the yellow-faced bumble bee (Bombus vosnesenskii); black-tailed bumble bee (B. melanopygus); yellow bumble bee (B. fervidis); the tricolored “fuzzy-horned” bumble bee (B. mixtus), and the California bumble bee (B. californica).

You can find complete and detailed species lists, along with keys and descriptions for identification in readily available online resources.^1,2  However, it is not always an easy task to identify bumbles due to wide color variation within species and confusing convergence of coloration among different species.  

Compare, for example, the black-tailed (also called red-rumped) bumble and several very similar-looking species also found here. Yes, there are specific differences you can see with close inspection – but at a glance, could you distinguish one from the other as they work among your flowers?

POLLINATION.   Along with honey bees, bumbles are excellent and important pollinators of wild flowering plants, garden flowers, berries and fruit trees, and of particular commercial and farm crops.  As generalist foragers, they do not depend on any one flower type and visit many different plants during every foraging day through the seasons.  They carry pollen in corbiculae (baskets) on the back legs.

Some plants rely on bumble bees for pollination, particularly because just like mason bees and many others of our native bee species, these furry foragers employ “buzz pollination” to collect pollen from certain types of flowers (about 6% to 8% of all flower species) that hold their treasure firmly inside tubular anthers to be released only through tiny pores or slits if they are vigorously shaken.

Holding on with all six legs and mandibles too, a bee vibrates its thoracic flight muscles, buzzing at a particular frequency between 100 and 400 Hz (bumbles are measured at about 270 Hz).³

Especially for the nightshade family (e.g., tomatoes, peppers, eggplants), some of the pea family (e.g., native lupine, vetch), the heath family (e.g., blueberries, cranberries, rhododendrons, azaleas) and many others, this special method is the most efficient way to extract and distribute pollen.

Accordingly, bumble bee colonies are often kept as pollinators in commercial tomato-growing greenhouse operations, for example, also in blueberry fields.  They are the only pollinators of potatoes grown commercially for seed.

In contrast to honey bees, bumble bees are cooler-weather foragers that are out working earlier in the spring and later in the fall than are our Apis mellifera. They can also fly when the light level is low, and therefore can extend their working-day outdoors, both in the morning and the evening, well beyond the hours of honey bee activity.

SOCIAL SYSTEM AND LIFE CYCLE.  Bumble bees are the only native bees in North America that are truly social. They live in colonies consisting of a single queen and her offspring of overlapping generations, with castes for division of labor: workers, queens, and drones (males). 

Colonies are generally small, some species with fewer than 50 individuals at maximum expansion, a few that attain a density of up to 500 or more, and a gradient of species with numbers in between.

Unlike honey bees, a bumble bee colony does not persist for years; rather, it has an annual life cycle that can last from February through November, or less.  That is, by summer’s end or sometime in the fall, the foundress queen along with all of her workers and male offspring will die. 

Only the new future-queens that are produced late in summer can survive the winter. After mating with a single drone from another nest and then feeding for several days, each queen finds an existing, shallow burrow or depression in a protected spot where she will remain in a resting, dormant state called diapause through the cold months.

When the overwintered queen emerges in the spring, she flies low to the ground, stopping often to examine potential nest sites. An existing rodent burrow is most often preferred, sometimes a cavity in a stump or a shallow basin under a stone, a wall, or a pile of leafy, twiggy debris.

She might instead choose a birdhouse with or without an old nest inside, or some other opportune spot that meets the requirements for safety and comfort.

In the new nest, the queen produces wax to build the first few brood cells in the form of urns. Both pollen and nectar she collects will be stored inside each one, and her first eggs laid directly upon the food supply to allow the hatching larvae ready access to it.

Like a mother hen sitting on her eggs, the queen perches atop the precious wax pots, warming the eggs and the larvae inside as this first generation of her colony develops. To generate heat, she vibrates her thoracic flight muscles without moving her wings, reminiscent of “heater bees” in our honey bee hives.

After 4-5 weeks, small workers emerge and take over most of the foraging and hive work to raise a series of generations during the spring and summer, leaving the queen to her egg-laying role.

The last generation consists of the reproductives. After mating, the drones never return to the parental nest, whereas the mated queens avail themselves of is protection each night until retiring to their own small overwintering nooks, continuing the cycle.

WHAT’S IN A NAME?  The genus name, Bombus, which was assigned in 1809, derives from the Latin word for a buzzing or humming sound, borrowed from ancient Greek βόμβος (bómbos).⁵

Although this type of bee was called interchangeably bomble (from the genus name), bumble, or humble bee in popular parlance, even domble bee in an English provincial dialect,⁵ Charles Darwin and his mid-19^th century contemporaries used only the common name of humble bee in their publications. 

By the mid-20^th century, the transition from humming humbles to bumbling bumbles was completed “once and for all,” perhaps in part as the fascination with natural flight and advancing aeronautical engineering perpetuated the notion that it is impossible for this genus of bees to actually FLY with such small, sideward-flapping wings to carry such a rotund, chubby body into the air. 

That is, the name bumble bee had come to represent a rather belittling view of these bees and their style of flight, which was seen as “bumbling” (as in fumbling, wobbling, wholly ungraceful) as they moved among the flowers.  However….. there is one more thing to learn about so-called bumbling bees.

THE FLIGHT OF THE BUMBLE BEE. “As the story goes, in the early 1930s a biologist asked an expert in aerodynamics with whom he was dining why bumblebees were able to fly. The latter promptly took a serviette and scribbled down a calculation based on the weight and the wing area of a bumblebee: his conclusion was that it couldn’t generate enough lift to fly.

“If a bumblebee were to be as large as an aircraft and constructed like one, it would indeed be unable to fly.

“But it isn’t. This is because its wings, rather than being rigid aerofoils, consist instead of an extremely elastic and supple protein known as resilin. This can be stretched to three times its length without tearing, allowing bumblebees to move a relatively large mass of air using wings with a small surface area.” ⁶

Like other bees in flight, bumbles attain efficient “lift” because they rotate their wings in a circular motion, sweeping them forward and back at a rate of 200-250 beats per second rather than flapping them up and down.

They are in essence using a principle that is also employed by helicopters: the rotary motion of their wings gives rise to a vortex along the leading edge of each wing, and enables them to move not only forward, side to side, up and down, and even backward in the air.

And further, bumble bee wings have a feature that those of other bees apparently do not. They have a special joint that allows the wings to bend during flight, enhancing the amount of weight a flying bumble can lift:  its own body plus twice its weight in pollen.  As such excellent fliers after all, bumbles have been observed in flight high on Mt. Everest at 18,400 feet, and in laboratory tests, they have shown the ability to fly in thin-air conditions such as would be found at 30,000 feet!⁶

Bumbling bug or aerial acrobat, perfect pollinator or adorable addition to the garden fauna, Bombus bees are truly amazing!