Bumblebees: The Big Buzz Pollinator

Bumblebees: The Big Buzz Pollinator

by Anita B. Stone  Most of us are familiar with bumblebees, primarily due to their size, bright yellow and black colors, and loud buzzing. This calm, passive bee, of which there are about 50 species in the United States, is one of the largest native bees, with the queen being about twice the size of her workers. While most native bees are solitary bees, the bumblebee is an exception. According to the National Wildlife Federation, this social bee lives in small colonies of 50 to 400 bees.    

Bumblebees build their nests in the ground in leafy, shady, undisturbed areas. Since bumblebee colonies have an annual life cycle, they do not maintain hives during the winter, and they use nests for only one year. The bees, however, will take advantage of ready-made cavities around woodpiles, stone walls, under house siding, old bird nests, and abandoned rodent tunnels, constantly refurbishing with warm insulation. 

A bumblebee colony consists of a queen, workers, and male bees. The queen can choose how many of each she produces. Fertilized eggs become the sexually undeveloped female worker bees, while the unfertilized eggs become males. A worker bee’s life span ranges from a few weeks to a month or two, while the queen remains actively laying eggs for the entire year. In early fall, the colony produces new queens and males, which exit the nest, fly into the air, and mate, after which the newly fertilized queens go underground where they hibernate throughout the winter. The male bees die soon after mating, and all of the remaining bees and the old queen die at the end of the season. In spring, the young queen emerges and begins the cycle anew; she searches for a nesting site, gathers a ball of pollen, deposits fertile eggs, and waits while the larvae develop into her first batch of worker bees a new colony is created.   

Aside from their charm, bumblebees have many interesting and unusual features. They are gentle bees, normally harmless when foraging and, although they can sting, especially if defending the nest or themselves, they aren’t easily aroused. According to Professor Emeritus, Dr. William Hood, a retired entomologist at Clemson University, “If disturbed, however, guard workers can be quite aggressive and sting repeatedly.”  

Due to their rapid metabolic rate, bumblebees need a constantly available food supply. Their fast metabolism requires that they eat almost continuously, which places them in danger of starving if enough food is unavailable. Their flight speed enables them to visit hundreds of flowers each day, making them efficient pollinators and expending large quantities of energy, requiring a steady nutritional supply. The bumble bee’s flight mechanism is unusual; they have no muscles attaching their small wings to their hefty bodies, so how they launch themselves into the air had been a mystery for years. French entomologist August Magnum, in 1930, noted that bumble bee flight is impossible. However, research has disclosed how the bee tightens and relaxes its body muscles, squeezing its body in a pattern that induces the wings to lift. These movements push the wings up and down and also creates a front-to-back movement. The speed generated by this mechanism forms enough force to keep the bumblebee in the air for long periods. Michael Dickinson, professor of biology and insect flight expert at the University of Washington, says, “wing sweeping is a bit like a partial spin of a ‘somewhat crappy’ helicopter propeller.” Once in the air, how bumblebees find their food is another complex process.   

Bumblebees prefer wildflowers with blue, purple, and yellow tones. 

Some favorites: monkshood, native goldenrods, blazing stars, violets, monarda, penstemon, comfrey, gaillardia, echinacea, sunflowers, and lavender.   

Up before dawn and working until dusk, these workaholics of the insect world buzz, searching for flowers by odor, color, shape, and utilizing the electricity in the air and the electrical charge on their bodies. The electromagnetic energy that surrounds each flower is detected, aiding in flower location. Through another surprising ability, bumblebees can determine whether another foraging bee has already taken most of the nectar and pollen, thereby preventing a waste of energy.   

All bees are important pollinators simply by their lifestyle, whether they are social, solitary, leaf-cutting, mining, or any other bee group, with the possible exception of the parasitic cuckoo bees. With the current reduction in bee populations, attention has focused on the pollinating activity of bumblebees.

Besides their speed and flower locating skills, bumblebees have an unusually effective method of collecting pollen. After the worker lands on a blossom, she grasps the stamen with her jaws and vibrates her muscles, causing the release of additional pollen at every stop. Bumblebee pollination is essential for many flowers, fruits, vegetables, and early flowering trees. For the bumblebee, the sugary nectar provides energy, and the pollen collected provides necessary protein. Since they can regulate their body temperature by vibrating their wings, bumblebees can remain active in cool temperatures and early and late in the day, making them important for early flowering plants and trees.  

Two bumblebees on a yellow flower collects pollen

Unfortunately, the stressors of climate change, parasites, pesticides, poor nutrition, pollution, herbicides, and habitat destruction have the same negative effect on bumblebee numbers as on other vulnerable insects. Since bumblebees are critical for some commercial crops, a new business of bumblebee management has become increasingly important and profitable. Greenhouse growers and hothouse farmers can request the shipment of these commercially available bees. 

Despite various management solutions, all forms of wildlife are under siege from a variety of sources. According to The Center for Biological Diversity, there are no regulatory mechanisms to protect bees against habitat destruction or monitor pesticide threats. Habitat loss causes bumble bees to work harder for their food. 

The public can help provide sustenance for these bees by planting the flowers they need, staggering the planting so that blossoms are available throughout each season. Another helpful aid for bumblebee survival is to supply suitable nesting areas. It helps to leave a section of your landscape a bit brushy without raking, mowing, or tilling, allowing plant stems to remain through the winter season, which gives the queen an attractive place to start her new colony. Hopefully, with the public’s supportive activity, the charming and important bumblebee will flourish and continue its flight to delight in gardens, roadsides, fields, and farms.   

Sources: 

  1. Daniel Robert, “Detection and Learning of Floral Electric Fields by Bumblebees,’” (Clarke, Whitney, Sutton and Robert, University of Bristol) 
  2. Michael H. Dickenson, Cal. Tech, Professor of Biology and Insect Flight, also University of Washington and Brown University. 
  3. NCSW.edu/general entomology 
  4. Dr. William Michael Hood, Professor Entomology, Research Apiculturist, Clemson University 
  5. Sarina Jepsen, Xerxes Society for Invertebrate Conservation 
  6. Missouri Department of Conservation, mdc.mo.gov 
  7. Heather Hines, PhD. Department of Biology and Entomology, Penn State University 
  8. Debbie Hadley, “The Life Cycle of the Queen Bumble Bee.” Thoughtco.com 
  9. Rachel Winfree, Biologist, Department of Ecology, Rutgers University 
  10. Michael Dickinson, Professor University of Washington, flight control specialist 
  11. Robbin Thorp, Emeritus Professor of Entomology, University of California 

Originally published in the December2021/January 2022 issue of Backyard Beekeeping and regularly vetted for accuracy.

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