Western Bumble Bee

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We’re taking action to protect the Western bumble bee

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Your campaign will help scientists research why bee populations are declining
Your campaign will help scientists research why bee populations are declining
Together we can help protect the Western bumble bee
Together we can help protect the Western bumble bee

How We're Helping the Western Bumble Bee
Protect Dates: September 2013- August 2014


Details: Through the help of kids just like you, Earth Rangers and Dr. Cory Sheffield of the Royal Saskatchewan Museum are protecting the Western bumble bee. The donations raised for this Bring Back the Wild™ project are helping to:

  • Survey bee biodiversity and habitat use to learn about bees in Western Canada, add information to the Canadian Biodiversity Information Facility’s bee database and study the impact of pathogens
  • Study if access to different numbers of flowers affects the productivity of managed and wild bee colonies
  • Create awareness about how bees play a vital role in food crop pollination and why bee conservation is so important


A message from researcher Dr. Cory Sheffield…

“Bumble bees are large, charismatic insects found throughout Canada, and are considered very important pollinators of wild plants and many food crops. Several species, including the Western bumble bee, have shown significant declines in population size and distribution in recent times, but the causes are poorly understood. Through a partnership with Earth Rangers, our team hopes to survey for the Western bumble bee throughout its known range to discover new populations, suitable habitat and refuges, and help understand some of the potential reasons for its decline.”

bee researcher cory
Researcher Cory Sheffield

Check out the latest updates about Western bumble bees!


all about western bumble bees

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  • Unlike their cousins Western bumble bees have white patches of hair on their abdomen
  • They live in a variety of habitats, including flowering grasslands, savannas and alpine meadows
  • Western bumble bees eat nectar and pollen; carrying pollen from plant to plant, Western bumble bees are excellent pollinators making them an important part of the ecosystem
  • They are currently under assessment in Canada (COSEWIC); main threats include habitat loss and fragmentation, disease, pesticides, invasive species and climate change

western_bumblee_beeflickr_user_ mo.do
Western bumble bee. Photo credit: Flickr User Mo

Having round, fuzzy bodies and bright colours, Western bumble bees (Bombus occidentalis) are an endearing and essential part of the grassland ecosystems along the west coast of North America. One of 30 different species of bumble bees found in Canada, the Western bumble bee is easily distinguished from its cousins by unique white patches of hair on its abdomen. Like other insects, bees have three main body regions (“segments”): head; thorax and abdomen. These white hair patches are on the abdomen which is at the opposite end of the bee from its head. The black and yellow colour pattern on the bee’s body alerts potential predators to the bee’s ability to sting to protect itself.

The name “bumble bee” was given to this family of insects because of the humming sound they make when they fly. Contrary to popular belief, the humming sound is not produced by the beating of their wings, but by rapid vibrations of their flight muscles. Bumble bee wings act more like helicopter blades than airplane wings, they don’t just flap their wings, they twist them! Their tiny wings push the air downwards, lifting the insect up, allowing them to fly. Still, keeping their furry, robust bodies in the air is hard work. Bumble bees need to beat their wings an astonishing 200 times per second to stay airborne! It’s A LOT of work being a bee!

western bumble bee
Western bumble bee. Photo Credit: Flickr user Ano Lobb

The Western bumble bee lives in a variety of habitats including flowering grasslands, savannas and alpine meadows. These areas provide ideal feeding (“foraging”) ground for the adults, but Western bumble bees may also be seen in agricultural fields and searching for wildflowers on forest floors. Bumble bees are considered generalist flower visitors in that they visit and pollinate flowers from a wide variety of plant species, including food crops such as tomatoes, blueberries, cranberries and cherries, among many others.

To house the colony, Western bumble bees also require nesting sites. Typically, Western bumble bees nest underground or in dense tufts of grass. Some of the best nesting sites for Western bumble bees are abandoned rodent burrows. Near the end of the summer, the next generation of queens will begin searching for overwintering spots, sometimes choosing hollowed out trees or other underground animal burrows to wait out the winter months.

bumble bee pollen
Bumble bee

Bumble bees are not typically the target of many predators, perhaps due to the colour of their bodies which warn other animals to stay away. This warning colouration (“aposematic colouration”) is a good thing too because bumble bees have a very important role to play in our ecosystem.

Collection of nectar and pollen by the Western bumble bee makes them excellent pollinators. For flowering plants to produce seeds, they must exchange pollen with the same or different flowers of the same species. When bumble bees land on flowers in search of food, they inadvertently gather pollen from the anthers of the flower onto the hairs covering their bodies. Then, when they move to a different flower, some of this pollen is left behind on the stigma, fertilizing the egg cells of that plant. Once plant egg cells have been fertilized by pollen, the fertilized eggs develop into fruits containing seeds. When the seeds are released and germinate they develop into new young plants. Without pollinators like bees it would be difficult for many plants to produce seeds; in fact, some plants rely so much on bee pollination they cannot transfer their pollen in any other way. Although some plants are pollinated by other means such as by butterflies, flies, mammals or the wind, the humble bumble bee plays one of the most important roles of all in grassland ecosystems.

B occidentalis queen
Western bumble bee queen. Photo credit: Syd Cannings

Different castes (groups or classes) play different roles in a bee nest or colony. Three different castes make up the social structure of a bee colony and include the queen, workers and drones. It’s the job of the worker bees to collect pollen and nectar for the family. To aid them in pollen collection, they have a special “pollen basket”, called the corbicula, on their hind legs. It is a small depression surrounded by long hairs which help them carry pollen back to the nest. Upon their return, the worker bees share what they’ve collected. The nectar is a source of carbohydrates and the pollen is an excellent source of protein for the bee larvae in the nest.

Honey is also part of a bumble bee’s diet. Honey is formed when the bees ingest and regurgitate nectar a number of times. It is then stored in the hive for a day when the weather doesn’t allow the bees to collect other food sources. Bumble bees don’t make as much honey as honey bees because only the queen bumble bee overwinters. Therefore, there is little need for bumble bees to stockpile food like honey bees do.

Western bumble bees are considered generalist foragers, meaning they don’t depend on one flower for food. They collect pollen from a wide variety of plants such as Melilotus, Cirsium, Trifolium, Centaurea, Chrysothamnus and Eriogonum genera, which include thistles, clovers and wild buckwheats.

Female bumble bee digging out her nest hole. Photo credit: Pahazzard
Female bumble bee digging out her nest hole. Photo credit: Pahazzard

The Western bumble bee is a social insect that lives in very structured colonies. There are three classes, or castes, of Western bumble bees in any colony: the queen bee, worker bees and drones. In the early spring, queen bees emerge from hibernation in overwintering sites and look for places to build nests for their new colony. Once they find a good place – in an abandoned rodent burrow or dense grass, for example – the queen lays her first eggs and collects food for the larvae when they hatch. The larvae eventually grow into female worker bees, which assume the responsibility for caring for the nest and finding nectar and pollen for the colony as the queen lays more eggs. Near the end of the summer, new queens and male drones hatch—these male drones mate with the new queens, who will then seek out their own overwintering sites before the end of the fall. As winter settles in, the old queen, worker bees and drones die, leaving the next generation of queens to start new colonies the following spring.

western bumble bee bombus occidentails
Western bumble bee. Photo Credit: USGS Bee Inventory and Monitoring Lab
  • Under Assessment (COSEWIC) – No recovered strategy yet but IUCN has a special sub-committee examining this species in Canada
  • A combination of habitat loss and fragmentation, disease, pesticides, invasive species and climate change are threatening the Western bumble bee

As recently as 1998, the Western bumble bee could be seen over a wide range in the Western and central parts of North America, found throughout Alaska and continuing as far south as Arizona and New Mexico. Once a common sight, the Western bumble bee has begun to disappear from much of its historical range in recent years. This species is thought to be close to disappearing completely in many areas including California and Oregon. This rapid and alarming decline in the species’ population size is thought to have come about from a combination of threats that have been building up over several years.

As with most animals facing threats to their survival in the wild, the Western bumble bee has faced many successive years of habitat loss and fragmentation. Loss of habitat makes it more difficult for the bumble bees to find foraging and nesting sites, and the fragmentation of their remaining habitat into smaller patches means that what food remains is farther away and more dangerous to access. Habitat fragmentation can also make it more difficult for drones and queens of different colonies to mate with each other, leading to inbreeding and a loss of diversity.

Although loss and fragmentation of Western bumble bee habitat has made life more difficult for the species, they are also facing several other threats. Diseases introduced to wild bumble bees from ones raised in captivity in other parts of the world are infecting large numbers of colonies, as are non-native parasites like the tracheal mite and other disease-causing pathogens. Further threats come from the widespread use of pesticides—bumble bees are exposed to these chemicals when they attempt to feed on plants treated with pesticides or when the pesticides wash off farm fields and into nearby wild spaces during rainy weather. Invasive plant species that are pushing out native wildflowers are also continually decreasing food sources for bumble bees and many other pollinating insects.

If you want to learn more about insect pollination check out:



The Xerces Society for Invertebrate Conservation. The Western Bumble Bee. http://www.xerces.org/western-bumble-bee/

Colla SR, MC Otterstatter, RJ Gegear, and JD Thompson (2006). Plight of the bumble bee:  pathogen spillover from commercial to wild populations. Biological Conservation 129:461-467.

Koch J, J Strange, P Williams. Bumble Bees of the Western United States. US Forest Service and the Pollinator Partnership. http://www.fs.fed.us/wildflowers/pollinators/documents/BumblebeeGuideWestern2012.pdf

http://www.fs.fed.us/wildflowers/pollinators/documents/ConsMgmtNABumbleBees.pdf (page 5)

IUCN Red List. Bombus franklini. http://www.iucnredlist.org/details/135295/0

Encyclopedia of Life. Bombus occidentalis. http://eol.org/pages/1065134/details


BBC One. Richard Hammond’s Invisible Worlds: Speed Limits. “Impossible Flight”. http://www.bbc.co.uk/pogrammes/p007vs8p



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