Living the Scientific Life (Scientist, Interrupted)

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Common Eastern Bumblebee, Bombus impatiens.

This species is often relied upon to pollinate commercial food crops,
such as tomatoes, that are often grown in agricultural greenhouses.

Image: Wikipedia [larger view].

The Bumblebees, Bombus species, are among the most popular of all insects. Their black-and-yellow fuzz, large round bodies, and bumbling, buzzing flight make them appear almost cuddly, almost like the “teddy bears” of insects. I have many childhood memories of watching these appealing gentle giants move from one bright flower to another, carefully gathering pollen grains and sipping nectar along the way, gently rebuffing occasional pokes from inquisitive fingers.


A plumose hair.
Image: Orphaned.
Please contact me with attribution information.
Bumblebees are easily identified on the basis of several physical characteristics; their distinctive color patterns and their rotund, fuzzy bodies. Nearly all species have at least some black on their bodies, and most have alternating black and yellow bands or splotches, but some species have white, orange or red in addition to, or instead of yellow, while others may be entirely black. Their large round bodies are completely covered with soft fuzzy plumose hairs, a characteristic that they share with several other hymenopterans according to Brian L. Griffin’s delightful little book, Humblebee Bumblebee: The Life Story of the Friendly Bumblebees & Their Use by the Backyard Gardener. However, Bombus are distinguished from other bees by the shape of the female’s hind legs. Each hind leg is specially modified in females to carry pollen; it has a bare concave surface surrounded by hairs, known as a corbicula or more commonly, as a pollen basket. In contrast, other similar bees have completely hairy hind legs.


Bombus corbicula (arrow).
Image: Matthew P. Kweskin,
The Evergreen State College.
Bumblebees occur throughout the Americas and Europe. Bombus is comprised of more than 250 known species that are primarily found in northern temperate, subarctic and subalpine regions, ranging into cold areas where other bees are not found, although a few species are endemic to tropical regions of South America as well. The reason for this wide distribution is because Bumblebees regulate their body temperatures through solar radiation, shivering, and radiative cooling from their abdomens, as you will learn when you read the excellent book, Bumblebee Economics, written by one of my favorite scientist-writers, Bernd Heinrich.

Similar to many other bees and wasps (the Hymenoptera), Bumblebees are social insects. However, unlike the domesticated honeybee, Apis mellifera, whose nests are comprised of hundreds of thousands of individuals, Bumblebee nests typically number between 50 and 100 individual and rarely exceed 500 individuals, although some colonies may surpass 1000 individuals in tropical climes. Additionally, while a generally large percentage of the entire honeybee hive successfully overwinters, only newly fertilized Bumblebee queens survive the winter. Early each spring, young Bumblebee queens forage and build their colonies after they awaken from hibernation. The young queens raise their first offspring alone while also foraging, until this first generation can take over babysitting duties and then can begin collecting nectar and pollen themselves.

A view inside a Bumblebee nest reveals the queen surrounded by workers
all atop the wax structure of the nest. Open wax pots contain nectar and pollen.
Wax covered clumps contain immature bumble bees. The structure is much
less organized than the perfect symmetry of honeycomb created by honeybees.

Image: Elaine Evans, University of Minnesota Extension [larger view].

Despite my fondness for and attentiveness to Bumblebees, I consider myself lucky when I discover one of their nests. Bumblebee nests are typically located in abandoned mouse holes, but I have found them in all types of objects, including attic insulation, compost piles, abandoned teapots and even in styrofoam refrigerator boxes. Early one spring several years ago, I discovered an active bumblebee nest after I bumped into a precariously dangling chickadee nest box. Within seconds, approximately one dozen small black Bumblebees with yellow and orange stripes greeted me with a soft hum. Fortunately for me, most Bumblebee species rarely sting, even when provoked, unlike the more aggressive domesticated honeybees. The young bees buzzed inquisitively around my face for a minute or so before wandering off to pursue their pollen- and nectar-gathering duties for the day.

As you will learn from Stephen Buchmann and Gary Nabhan’s important book, The Forgotten Pollinators, Bumblebees are important pollinators for a variety of food plants that are native to the northern latitudes such as potatoes, blueberries, cranberries, eggplants, kiwi fruits (Chinese gooseberries) and raspberries, and for important crop plants such as red clover, alfalfa, and cotton. Further, Bumblebees are the only insect capable of pollinating the Solanaceae, a family of plants that includes economically important crops such as tomatoes, peppers and tobacco. Approximately 8% of the world’s known 250,000 species of flowering plants, the angiosperms, rely exclusively on Bumblebees for pollination.


Bumblebee on a Foxglove blossom.
Image: Mike Montalvo.
Bumblebees have several special attributes that uniquely adapt them for pollinating “their” flowers. First, Bumblebees have longer tongues than domesticated honeybees. Their tongues allow Bumblebees to pollinate flowers with long, narrow corolla tubes — which are found in many flower species that are endemic to North America such as foxglove and fuchsia. Additionally, the large size of Bumblebees enables them to push their way into flowers that protect their nectar reservoirs with “trap doors” or other barriers, such as snapdragons. Further, because Bumblebees are cold tolerant, they visit flowers much earlier in the year than can domesticated honeybees, which are native to Africa. In fact, Bumblebees can be found flying when the cloud cover is more than 70% or when ambient temperatures are cooler than 15 degrees Celsius — either condition is sufficient to keep honeybees snuggled together in their hives. Amazingly, bumblebees have been reported to actively forage during the winter!

The most remarkable Bumblebee characteristic is their special ability to release tightly held pollen from many important crop plants using sonic vibrations. This ability — unique to Bumblebees — is commonly known as “buzz pollination” or “sonication.” Using sonication, a buzzing Bumblebee’s body shakes rapidly, thereby releasing pollen from tomato blossoms hundreds of times faster than can a honeybee. Their energetic high-pitched buzzes are produced by rapid contractions of their flight muscles while they are decoupled from their wings. These muscular contractions produce physical vibrations of approximately 400 Hz that are transmitted throughout the hollow pollen-containing anthers of the flower, releasing clouds of golden pollen. The Bumblebee’s fuzz captures this airborne pollen, some of which is distributed to nearby flowers by the bee, thereby guaranteeing a new crop of tomatoes for humans to enjoy. But most of this pollen is gathered into so-called “pollen baskets” on the Bumblebee’s hind legs and they deliver this collected pollen to the hive where the bees later consume it. Because Bumblebees consume pollen in addition to nectar, they visit these so-called “buzz blossoms” that are typically ignored by honeybees, who actively seek out flowers that provide a nectar reward for their pollinators.

The Bumblebee’s intense buzzes also makes a strange noise, somewhat reminiscent of the sound produced when one person gives another a “raspberry” or a “Bronx cheer” (which also suggested the peculiar title for this essay).

Considering their environmental and economic importance as pollinators, one might expect that many Bumblebee species have been domesticated, as were their cousins, the honeybees. Unfortunately, this is not the case: with the exception of several tropical species, Bumblebee hives do not over winter so their colonies are much smaller than honeybee hives. As a result, they do not amass large stores of honey necessary to support their large populations through the winter — these are the same honey stockpiles that are seasonally raided by beekeepers with a sweet tooth. Despite the fact that Bumblebee honey is delicious, they produce such small amounts that they are not attractive to commercial beekeepers. However, several species of Bumblebees have been domesticated for use as pollinators, including Bombus impatiens, which is the main species currently used in North American greenhouses especially those producing “hothouse tomatoes”, and the large Earth Bumblebee, Bombus terrestris, which is native to Europe.

A wild Bumblebee, Bombus vosnesenskii (right), and a domesticated honeybee, Apis mellifera (left), forage together on a sunflower.

Image: Sarah Greenleaf [larger view].

Unfortunately, most Bumblebee species are declining or are endangered in the wild due to indiscriminate use of broad-spectrum pesticides, as well as habitat destruction and the introduction of foreign pests and diseases. This has resulted in a concomitant reduction in native plant species that depend upon the unique pollination abilities of Bumblebees. But gardeners and property owners can help conserve Bumblebees by providing them with a safe home: by not using any pesticides on your property, by leaving rock and wood piles and compost piles intact and undisturbed, and by growing plenty of wildflowers. Further, if you do discover a Bumblebee nest on your property, please leave it alone, except to move it to a more private location, if necessary. If you absolutely must move a Bumblebee colony out of their chosen nesting container, then you should provide them with a small wooden or styrofoam box that has a small entrance hole, preferably a chickadee or wren nestbox.

It is my hope that this little essay will help people to become aware of the importance and the plight of Bumblebees so they will act to preserve these amazing insects and the many native plants that depend upon them.

======

Thanks to my pal, Liz, for fact-checking this document.

Sources:
NOTE: I highly recommend all of these well-written and informative books to interested readers

Bumblebees (Naturalists’ Handbooks 6) by Oliver E. Prys-Jones & Sarah A. Corbet (Richmond Publishing, UK; 1991). Obtained in Seattle courtesy of Flora and Fauna Books.

Bumblebee Economics: Revised edition, by Bernd Heinrich (Harvard University Press; 2004; originally published in 1979).

Humblebee Bumblebee: The Life Story of the Friendly Bumblebees & Their Use by the Backyard Gardener, by Brian L. Griffin (Knox Cellars Publishing; 1997).

The Forgotten Pollinators by Stephen L. Buchmann and Gary Paul Nabhan (Island Press; 1997).

The Natural History of Pollination by Michael Proctor, Peter Yeo and Andrew Lack (Timber Press; 2003).

Insects and Flowers: The Biology of a Partnership by Friedrich G. Barth (Princeton University Press; 1985).

Comments

  1. #1 Ian
    April 2, 2009

    It’s comforting to know when we wish to find out what the buzz is, you have the answers ready!

  2. #2 Julie Stahlhut
    April 2, 2009

    One of my favorite things about spring: It’s when the overwintering Bombus queens become active and start searching for nesting sites. There’s nothing like taking a walk in the woods and hearing the loud buzzing of a big, low-flying mama bumble checking out possible homesteads.

  3. #3 Tom Manney
    April 2, 2009

    We followed these two around the yard from one thistle to another. The honey bee appeared to be “harvesting” the pollen from the bumble bee’s hairs as the latter came in contact with each blossom.

  4. #4 brendan
    April 2, 2009

    In regards to the picture of the Honey Bee next to the Bumble Bee. It interesting to note, that the Bumble bee will not store food reserves as opposed to its friend in the picture, making it susceptible to food shortages.

    Brendan
    http://www.wildramblings.com

  5. #5 Ian Paulsen
    April 2, 2009

    HI ALL:
    If you’re interested in attracting Bumblebees to your garden try one of these:

    http://www.nhbs.com/title.php?bkfno=179144&ad_id=482

    I wonder if they are available in North America?

  6. #6 Tim
    April 2, 2009

    Just because Wikipedia is open-access and freely editable doesn’t mean you don’t need to cite it! Kind of undermines all the hard work people put into writing the articles.

  7. #7 "GrrlScientist"
    April 2, 2009

    tim — the informational sources i relied upon are my fellow grad students, several of whom studied bumblebees, as well as my own experience and readings (which are considerable) since i almost studied bumblebees for my own graduate work. further, this piece is the edited and condensed version of several essays i originally wrote for the biology department newsletter when i was in grad school, which happens to have occurred before there was a wikipedia.

  8. #8 biosparite
    April 2, 2009

    Another aspect of bumblebee econ: when the queen starts out in the spring, she must operate for awhile sans helpers. So the first brood of young do not get the greatest of care and thus do not attain the larger size of later offspring which benefit from the attention of helper bees. I could see the results in my Houston garden, since the spring bumblebees could fit into the corolla of Torenias (wishbone flowers); but later generations of bees were too wide to gain entry, becoming nectar thieves that penetrated the corolla from the outside down near the sepals. By the way, I have heard that a blogger near and dear to us readers would pet bumblebees when she was a girl wandering around outside in Eastern Washington.

  9. #9 Michelle
    April 2, 2009

    Thanks for the great article!

    One of my favorite things about spring is finding a bumblebee (now I know it’s a queen) asleep inside a crocus.

    My second-favorite kind of bee is the Carpenter Bee. Talk about some great adaptations – completely docile, but with killer mandibles.

  10. #10 Juuro
    April 3, 2009

    In my yard and around the garden I have largish patches of monkshood (Aconitum spp.). From the first blossoms to early autumn, it is never silent there. I have been consistently amazed at the hours the bumblies keep.

    Very nice reading. Thank you!

  11. #11 clheiny
    April 4, 2009

    Thanks, GrrlScientist! That makes a great morning read.

  12. #12 rdb
    April 4, 2009

    I don’t think that all the Solanaceae need bumblebees as pollinators. Australia has native Solanaceae, like Bush Tomatoes, Kangaroo apples, Native tobacco, but doesn’t have bumblebees, except I think for feral escapees from greenhouse trials in Tasmania, Solanum crops (tomatoes, potatoes, …) and deadly nightshades all grow well enough.

    http://www.aussiebee.com.au/bumblebeesightings.html

  13. #13 Centers and Squares
    June 6, 2009

    I stumbled upon your delightful post by way of a blog carnival. It caught my eye because it seems to be a really good year for bumblebees in Massachusetts – there seem to be quite a lot of them around and they look bigger than usual (my completely unscientific observations!). I’ve had several conversations with people about it already this spring.

    Since I’m not terribly fond of anything that stings I was happy to read about their gentle dispositions. I will look differently at them now. I appreciate the reference list too and find the title “Humblebee Bumblebee” virtually irrestistible!

    Liz

  14. #14 Matt Sarver
    August 2, 2009

    Great post! I’d like to add another really valuable (and readable) reference: The Natural History of Bumblebees: a Sourcebook of Investigations, by Carol Ann Kearns and James Thomson (2001). It’s an excellent brief overview of Bombus natural history.

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