May 21, 2010

Following Bumblebees

By Margaret Gillespie, Illustration by Cheryl Johnson

Imagine my surprise when I discovered that bumblebees had nested in a hole at the base of a second story porch right next to my apartment entrance. To be more precise, this meant that they buzzed right past my head as we all retired inside at dusk! It was easy to get used to – after all, bumblebees, ladybird beetles, and butterflies are the insects almost universally liked by humans, and I am a dedicated insect fan. The following year I was disappointed when none took up residence in the same spot, but I soon discovered a more challenging nest location! Eager to get natural fertilizer on my garden, I dug my shovel deep into the compost pile and out came bumblebees! Fortunately this was a very different experience from doing the equivalent to a wasp nest, and the bumblebees settled down quickly once I backed away. What stayed with me was the intense desire to learn more about how bumblebees live and work.
Do bumblebees bumble? “Bumble” describes their somewhat clumsy way of flying or could also come from the humming sound they make. This buzzing noise logically would be from the beating of their wings, but bumblebees with motionless wings still buzz! Apparently the vibrations from flight muscles in the thorax produce the buzz, and in cool weather, this activity is necessary for warming the bumblebee adequately for flight. Speaking of warmth, bumblebees are covered with soft fluffy pile often in black and yellow warning bands. They win the bee prize for cold weather flight, active at 50 degrees Fahrenheit and have even been recorded flying at 32 degrees. Do you think you could outrun one of these bumbling insects? Try zigzags at 10 miles per hour – the bumblebee will come out the winner!
Take a close look at a bumblebee – they are experts at collecting and transporting nectar and pollen. As a bumblebee visits a flower, its long tongue emerges to sip nectar which is then stored in its honeystomach, a storage compartment in the abdomen. The honeystomach is not part of the digestive system although some nectar can be transferred to give the bumblebee needed energy. Pollen, a source of protein, can be taken directly from the flower or groomed from the insect’s fuzzy body after a flower dusting. In either case, pollen is packed into a “pollen basket,” officially called the corbicula. This structure is a concave shiny surface on each rear leg which will be yellow and bulging when full of pollen. Want to tell a male from a female bumblebee? The easiest way is to check for a pollen basket – only the queen and female workers have them.
What are some tricks of the bumblebees’ trade? Sometimes pollen is difficult to extract from plants like tomatoes and blueberries, but bumblebees are experts with a technique known as “buzz pollination” or sonication. By vibrating their flight muscles while holding onto the flower (and thus making a really loud buzz), bumblebees shake the flowers enough to release pollen. Bumblebees also scent mark flowers so they can tell which ones have been recently foraged. Some plants like lady’s slippers depend upon bumblebees for pollination – these heavy, powerful insects may be the only ones strong enough to enter their flowers. Another way that bumblebees benefit flowers results from an electrostatic charge that builds up in a flying bumblebee. When the insect lands on a flower, pollen is attracted from the grounded flower to its fuzzy body. At the next flower, the pollen carried by the bumblebee is still charged and transfers to the most grounded part of the flower – yes, the stigma. Pollination happens!
As I write this article in early spring, queen bumblebees are searching for nesting sites. I hope one settles in an old rodent nest or hole or perhaps in a grassy mound close to where I live so that I can keep track of the colony’s progress. Once situated, the queen will forage for nectar and pollen and then begin to lay eggs. These fertilized eggs develop into female workers which take over housekeeping and foraging duties. By mid-summer the colony will be at its height which may be only 50 bees. As summer wanes, the colony enters its final stage when the queen lays unfertilized eggs that develop into males. She also lays fertilized eggs that receive extra food and care, resulting in new queens. Males soon leave the colony and find shelter at night in and under flowers. Look for their dew-covered, lethargic bodies in the early morning! By scent marking certain areas, males attract the new queens. Once mated, males die while queens search for hibernating spots. These new queens are the only ones to survive the winter. Next spring they will be ready to start their own colonies.
Would you like to follow a bumblebee? First, listen for the buzz which leads you to a busy bumblebee on a flower. Is she carrying pollen? What kind of flowers does she prefer? How is she collecting the nectar and pollen? Are you getting too close? She may raise her central leg in your direction to let you know you are in her space. Then, zoom, off she buzzes, leaving you with the gift of having shared a few moments in the life of a bumblebee.

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