Genus: Bombus

There are over 250 Bombus species in the world!

Species in the genus Bombus are commonly known as bumble bees! Bumble bees are unlike other bee genera because they are most diverse in "cool temperate or montane situations" 1. The highest bumble bee diversity is found in the mountains around the Tibetan plateau. Bumble bees can be found in North America, South America, Europe, and Asia 2. Species in the genus Bombus previously were commonly called humble bees. They got this commony name because of the humming sound they make while flying. The common name of bumble bee became more widespread over time referencing their rather haphazard and clumsy flying patterns.

Bumble bees mainly feed on pollen and nectar from plants. This makes them both palynivores (an animal that eats pollen) and nectarivores (an animal that eats nectar). Pollen provides bumble bees with protein and fat. Nectar provides bumble bees with carbohydrates in the form of sugar and starches.

Bumble bees are capable of buzz pollination which is the only method of pollination for certain crops and flowers. Buzz pollination is when a bee grabs a flower with its pincer like mouth parts and vibrates her thorax to dislodge pollen from the flowers 3. Pollen will not dislodge from some flowers unless they are buzz pollinated. Some crops that require buzz pollination include tomatoes, potatoes, kiwis, eggplants, cranberries, and blueberries 4. Bumble bees are generalist pollinators, so they feed on lots of different flowers for pollen and nectar. This makes them valuable in their native habitats as they can pollinate many native flowers.

"The yellow-faced bumblebee (Bombus vosnesenskii)" by edward_rooks is licensed under CC BY-SA 2.0.

The photo shows a yellow-faced bumble bee (Bombus vosnesenskii) foraging with a ball of blue-grey pollen in its corbicula on its hind leg. A corbicula is commonly known as a pollen basket. The corbicula is a shallow indentation on the outside of the hind legs of some bees which is surrounded by stiff hairs. Bumble bees will compact pollen and store it in their corbicula for transport. The colour of the pollen ball within the pollen basket can tell you which flower the bumble bee has been foraging on.

The yellow-faced bumble bee is native in the Pacific Northwest. It is commonly found in parks and gardens. You can identify it by its yellow forehead, single band of yellow hair on the anterior area of the thorax, and single yellow stripe that is bordered by black near the posterior of the abdomen.

Most, but not all, bumble bees are social insects.

Most bumble bees, similar to honey bees, have two different types of female bees; the queen bee and the worker bees. The queen bee in bumble bees creates the nest, lays the first eggs, feeds and cares for her first batch of eggs and young bees (also known as brood), defends the early nest, and then only lays eggs after first brood has become adults. When worker bees emerge, they do all of the maintenance, defense, and foraging for the nest and usually don't lay eggs (more on that later). Related individuals working together like means that bumble bees can be considered social animals! In addition to this, bumble bees can be considered eusocial like honey bees because the reproductive labour and the colony maintenance are split between the queen and the worker bees, the workers and the queen cooperate together to take care of the brood, and there are multiple generations of adults in colony at some point in time 5. Bumble bees also produce males, but the male bees do not preform any labour. The only job of the males is to mate with queen bees before the winter.

While most bumble bees are social, some bumble bees are actually parasitic to their social bumble bee counterparts. These bees are known as cuckoo bumble bees. Cuckoo bumble bees invade the nests of social bumble bees and they must do it when the social bumble bee colony is large enough to support them, but not so large that they can kill the invading queen 1. When a parasitic queen enters the nest, they sometimes kill the social queen and force the workers to take care of their brood using both aggression and pheromones. In taking over the nest, the parasitic bumble bees do not have to spend the energy to create their own nest or collect pollen and nectar. And, because the brood of cuckoo bumble bees is only queen bees and males, the cuckoo bees do not have to spend energy on producing workers. Due to the way these bees must reproduce, cuckoo bumble bees are declining rapidly as social bumble bee species decline and many cuckoo species are endangered. Why should we care about these bees declining? Cuckoo bumble bees are beneficial because they pollinate plants, can be used to monitor the population of the host bee health, and reduce disease virulence in their host population 6.

This photo is of the cuckoo bumble Bombus rupestris. Its common name is the red-tailed cuckoo bumble bee. This bee invades the nests of Bombus lapidarius (aka., the red-tailed bumble bee) which is one of the most common bumble bees in the UK. The red-tailed cuckoo bumble bee can be 2.5cm (~1 inch) in length!

Bombus rupestris is growing in number in the UK. So, hopefully we can do more research on these bees to better understand cuckoo bumble bees as a whole!

"Trzmielec - Psithyrus rupestris" by Greenpeace PL is marked with CC BY-ND 2.0.

The life cycle of a bumble bee colony.

The colony cycle of social bumble bees is as follows...

The queen bee emerges in the spring after hibernating all winter. After emerging, the queen flies for several days and feeds on the nectar provided from early spring blooms. Queens then start to search for a nest site by flying low and crawling along the ground. Bumble bee queens do not make their own nests and, instead, search for preexisting nooks and crannies like rodent holes, hollow logs, bunch grasses, bramble patches, man made structures like bird houses, and many more (Williams et al., 2014). Bombus queens are able to withstand cool and wet weather in spring by shivering the muscles in their thorax and by walking along the ground. Here is a fantastic video by BBC earth that shows bumble bee queens heating up their thoracic muscles by walking along the ground using a thermal camera!

After a queen has found a spot to nest in, she collects pollen and nectar for the nest. She creates a wax cup that she puts a lump of pollen in, lays her eggs on top of the pollen, and creates a wax cell by putting wax over top of the wax cup. In addition to this wax cell, the queen also creates a wax pot to store collected nectar in and puts in reach of the wax cell (Sladen, 1912). The queen will then sit on top of the eggs and will shiver and move her abdomen to keep the eggs warm (Sladen, 1912). She also sips from the nectar pot to keep up her energy until the eggs hatch! When the eggs hatch, they are larvae and not adult bees. The larval stage lasts for two weeks before they spin a cocoon and pupate (similar to caterpillars becoming a chrysalis) for two weeks and, after two weeks have passed, adult worker bees emerge from their cocoons.

When the first workers emerge, the queen no longer leaves the nest. The workers do all the work the queen did by herself when she started the colony including provisioning the nest with pollen and nectar, keeping the eggs warm, feeding the new growing larvae, keeping the nest warm, and defending the nest. After the first brood is produced, the number of bumble bees in colonies grows rapidly.

After a large production of workers, the queen prioritizes the production of male bumble bees and new queens. Males leave the nest after pupating to mate with newly emerged queens from other colonies. Males do not forage for the colony. New queens will leave the nest to mate and forage during the day and will often return at night. They are foraging to build up fat stores before the winter.

The new queens mate with usually one male from another nest and then prep for the winter. After mating, queens search for a place to overwinter in. This can be the nest where they were produced, in a hole they have dug into the soil, rodent burrows, or in compost piles as some examples. The overwintering site must be below the frost line or warm enough so that the queen does not freeze and die during the winter. The new queen will hibernate for many months, which is why it is crucial that new queens build up fat stores. The worker bumble bees, males, and old queen bees all die off before winter begins.

"Bombus Latreille, 1802" by NHM WASPS is licensed under CC BY 2.0.

This photo shows a preserved bumble bee nest. The enclosed cells that are a brighter yellow would contain the developing pupa. The large brown lumps would contain eggs or larvae that have just hatched. The open cups usually contain honey and pollen for the nest, but they are not present in this model.

This preserved bumble bee nest also has several bumble bee models on it. The large bee in the center represents the queen bee. The small bees in the rest of the nest are the worker bees. Finally, several models of newly emerging adult bees have been added into open cups.

Some interesting bumble bee species.

Bombus occidentalis, also known as the western bumble bee, is a species that was once abundant, but has experienced rapid declines in its population 7. This bumble bee used to be common in British Columbia, southern Alberta, and southern Saskatchewan and 30-40% of its range was in Canada. Sadly, the decline of this bee was likely due to stressors - including an increase in the number and type of pathogens in wild and managed B. occidentalis populations, loss of floral and nesting resources, pesticides, and changing climate 8. Additionally, three other bumble bees started to decline around the same time as B. occidentalis likely due to similar stressors: Bombus affinis (aka the rusty patched bumble bee), Bombus franklini, and Bombus terricola.

Bombus dahlbomii is one of the world's largest bees with queens of this species reaching 40mm in lengt! Bombus dahlbomii has striking orange hair all over it's body with a black face and black legs. This bumble bee is native to Chile and Argentina, but is most abundant in Patagonia 9. Unfortunately, this bee has become endangered. Bombus dahlbomii populations started to decline after two managed bumble bee species were introduced from Europe and its range has continued to shrink to this day 10.

Bombus cockerelli is one of the world's rarest bumblebees. This bumble bee was likely first found in 1899 near the Rio Ruidoso river in New Mexico, but was not considered a real species for decades due to it's rarity and a very small range 11. There are only 34 known specimens of this bumble bee and some of these specimens were collected over 120 years ago. On top of very few species being found, all specimens have been found in a 800 square kilometer region which is roughly the area of New York City. This is the smallest natural range of any known bumble bee species in the world. With these two factors in mind, it's no wonder that scientists were skeptical of this bees existence until genomic testing and an inventory of Bombus cockerelli museum specimens could be performed.

This collage allows you to see just a few of the many bumble bee species! As you can see, bumble bees can have hair that is red, orange, yellow, black, white, or a combination of any of these colours. Most bumble bees do not have the black and yellow stripes that they are usually associated with. These are all photos taken by Sam Droge for the U.S. Geological Survey. Pictures are not to scale.

A) Bombus dahlbomii, B) Bombus auricomus, C) Bombus bifarius, D) Bombus rufocinctus, E) Bombus vosnesenskii, F) Bombus occidentalis, G) Bombus flavifrons, H) Bombus terrestris, I) Bombus eximias.

Wild species of bumble bees are on the decline.

Bumble bees are extremely important pollinators for all manner of flowering plants. As we discussed earlier, they are capable of buzz pollination while honey bees are not. Buzz pollination is needed for between 15,000-20,000 different flowering plant species 12. Buzz pollination is what makes bumble bees some of the best pollinators of blueberries and cranberries! Native bumble bees also pollinate important native plants that are used by other bees for shelter 1.

Bumble bees are on the decline, but you can help by reducing pesticide spraying and not keeping managed bees when possible. The application of insecticide harms both pest insects and beneficial insects like bees and butterflies. An easy solution is to use natural insect repellents in your garden and to promote natural gardening when possible. The introduction of managed bees, like honey bees (Apis mellifera) and certain introduced bumble bees, spread pests and pathogens and compete with wild bumble bees for food 13 14 15. For wild bees, the fewer managed bee nests or hives that are present in an area, the better! This is not to say we can't keep bees at all, but please note that keeping managed bees will not help wild bee populations.

If you're interested in actively helping wild bumble bees, the best things you can do are become knowlegeable about them, plant a large variety of flowers that flower throughout the year in your garden (if you have one), and to provide nesting spaces that bumble bees can use. You can find information about creating rock piles or wood piles that bumble bees can use nest in here.

Bumble bee short facts

Some bumble bees have long tongues, while others have short tongues. Long tongued bees can reach deep into long narrow flowers, while short tongued bees tend to forage on smaller flowers 1 16.
Short tongued bumble bees sometimes rob flowers of their nectar. This behavior is when a bee pierces the base of a flower to reach nectar that may be out of reach. This means the bees don't enter the flower and covered in pollen, so this is bad for plant reproduction.
In bumble bees, workers are capable of laying eggs like the queen. Due to their genetic makeup, all eggs laid by workers will become male bumble bees.

Page information

Author: Melissa Platsko

Date published: June 16, 2022

Date last edited: August 11, 2023

References

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