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Washington's Humble Bumble Bees

Updated: Dec 12, 2021

A Bombus calignosis bumble bee with large pollen sacs flies away from a blackberry flower
A Fogbelt bumble bee worker (Bombus caliginosis) showing how she stores and carries pollen she collects on her rear leg. Bumble bees can carry almost 40% of their weight!

We are rapidly coming to appreciate how important our local pollinators are for keeping our plants and ecosystems healthy. We are also learning how our native pollinators are in decline. This article focuses on Washington’s bumble bees as an introduction to our native bee community.

What is a pollinator?

In biological terms, a pollinator is an agent that physically moves pollen from one flower to another, enabling seed set. Some flowering plants use wind or other physical methods to move the pollen: think ragweed and conifers. Worldwide, as well as here in the US, approximately 80% of flowering plants use an animal for pollination. While there are birds, bats, beetles, and butterflies that pollinate, pollination of most flowering plants (~75%) is primarily done by native bees such as our bumble bees.

Bees are very important pollinators. A few bee species are social, like honeybees and bumble bees, but the vast majority (~90%) are solitary or brood parasites.

Why do bees make good pollinators?

The orange abdomen of a Hunt's bumble bee protrudes from a penstemon flower
Hunt’s bumble bee (Bombus huntii) foraging for pollen and nectar.

Why, out of all the animal groups that pollinate plants, are bees the most common pollinators? This is due, in part, to two behaviors exhibited by most bee species. The first is constancy. When a young bee leaves to forage for the first time, she has never found nor collected nectar or pollen. When she encounters a flower, she figures out how to get rewarded. Once she learns, she will seek out the same flower species until she has collected all the pollen she can carry—or she can’t find any more of that flower species. Then she will transition to another flower species.

This constancy behavior has resulted in native plants evolving to increase success in attracting native bees and thus their likelihood of pollination and associated seed set success. Other visitors that do not show such flower species fidelity are not as much help.

Bombus vancouverensis with wings spread, takes flight from an aster flower
Bombus vancouverensis (previously knows as B. bifarius) (This bumble bee is commonly known as the Two form bumble and is relatively abundant on the east side of Washington.

The second reason bees are such good pollinators is that they deliberately collect pollen and nectar to feed their young (and themselves). Butterflies, flies, beetles, and wasps typically do not gather pollen when they visit flowers—they are mainly after the nectar. The pollen they transport has been brushed onto them by happenstance. Bees, however, feed pollen to their young, so they are purposefully collecting pollen.

When bees carry their pollen load from flower to flower of the same species, it greatly increases the chance for successful pollination to occur. By actively collecting pollen and by exhibiting constancy our native bees make dependable pollinators for many of our native plants.

Learning about bees

Bumble bees are intriguing insects. With their stout bodies and dense hairs, they are adapted to cool and wet climates. Bumbles can deliberately raise their body temperature well above ambient, enabling them to fly early in the morning before most other insects are active. They can fly in high alpine meadows and even above the arctic circle in a snow storm. Bumble bees have a proclivity for higher latitudes and elevations, and for cool damp climates. It is no wonder that Washington state has about half of all the bumble bee species found in the US—25 species and counting.

Like native plants and birds, recognizing the different species of bumble bees is an enjoyable pastime and an important element in learning more about them. Questions that got me started on this learning journey included:

  • How many species do I have using my garden?

  • Which species like which blooms?

  • What types of bumble bee mimics are in my garden?

  • Is this bee a queen, a worker, or a drone? How do I tell?

  • Does my garden attract bumble bees or honey bees or both?

We have put together a website on Washington’s bumble bees. A major focus is on species identification. Other sections address gardening, conservation, and related resources. Visit our site to get these and more questions answered about Washington’s humble bumbles.

Bees and your garden

A bright yellow Bombus morrrisoni hovers near a pink cluster of flowers
Morrision’s bumble bee (Bombus morrisoni), a very uncommon species of our arid lands and their urban areas

While bumble bees “can” sting, unlike honey bees or some species of wasps, bumble bees in your garden are very unlikely to sting you. When bumble bees are actively foraging, they are not defending a nest. They are focused on harvesting pollen and nectar for their young. It is much safer and more efficient for them to move away if they get disturbed. I find the sting (happens sometimes when removing one from my insect net) to be very minor—nothing as painful as a honeybee sting. Unlike honeybees, stinging does not result in the death of the bee or the venom sac left at the injection site.

Some species of plants require bumble bees for successful pollination. This is true of both native and cultivated species. It is expensive for plants to generate pollen and nectar. To a flowering plant, a worst-case scenario is an insect coming in, drinking the nectar, eating the pollen, and then going to a flower of a different species.

Because bees show constancy, plants that attract more bees have an increased chance of pollination. To reduce the chance that an unwanted nectar-stealing insect will show up, some plants have stamens that will not release their pollen unless they are vibrated at just the right frequency. Bumble bees vibrate their wings to create the required frequency. This behavior is called buzz pollination. Tomatoes are an example of a familiar plant needing buzz pollinator for best fruit set.

Bumble bees are the perfect introduction into our native pollinator community. They can be common, even in urban areas with minimum habitat. They will come if you create an inviting space. They are relatively easy to identify—with a little practice. Most gardens will have 3–4 bumble bee species—and only a couple of them will be regulars. This provides a chance to learn which are in your neighborhood and to become aware of species changes over time.

Two bumble bee species to keep your eyes out for are the Western bumble bee (Bombus occidentalis) and the invasive Common eastern bumble bee (Bombus impatiens).

The Western bumble bee suffered large declines back in the 1990’s following the release of European raised captive Western bumble bees into commercial tomato greenhouses for their buzz pollination capabilities. The commercially raised bumbles are suspecting of infecting the wild populations with European pathogens. Western bumble bees were spotted in the Puget Sound region in 2012, marking the first sighting of this species in almost a decade. It is slowly increasing its presence on our landscape but still remains a species of concern.

Bombus occidentalis in flight amongst lupine flowers
The Western bumble bee (Bombus occidentalis)can be easily identified by the white stripe at the rear of the abdomen. It can be found statewide, but has a stronger presence on the east side of the state

The Common eastern bumble bee was first documented in Washington State at Peace Arch Park, near the Canadian border, about 3 years ago. It has already been detected just north of Seattle. It is an east coast species raised for commercial greenhouse operations in British Columbia that escaped into the wild, became established and is now moving into our state.

Bombus impatiens upside-down on the white blooms of winter heath
The Common eastern bumble bee (Bombus impatiens) can be identified by the large black abdomen having a single light stripe at the top of the abdomen.

Help Save our Bees!

While many conservation efforts are only effective at a regional scale, gardening for native pollinators and creating backyard wildlife habitat is effective at both the individual yard and community level. Ensuring a diversity of blooms are available for pollinators from early spring through fall supports and enhances many different species of our local pollinator community.

While quite a few jurisdictions and agencies (e.g., WSDOT) are already incorporating pollinator friendly practices, more can be done. Writing and asking your local elected officials to continue to consider native plants and pollinator friendly plantings as part of their public lands’ management is an easy ask and relatively easy for the community to support.

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Richard Mathes
Richard Mathes
Jan 07, 2022

Well written; great photos. I raise mostly native plants for bees in Seattle; yes Grindelia integrifolia and the asters are great in fall; I also raise Madia elegans, an annual, up to 5 feet, that blooms until frost, although blossoms get smaller in cold. You identified the bees I see - I just have not learned a lot of names outside of Bombus xx.

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