It’s a Bumblebee’s World
Spring has nearly sprung, and the bumblebee is its harbinger, explains researcher Kent McFarland.
Kent McFarland was one of the subjects of our recent feature on the decline of Vermont’s (and other) bumblebee species, “To Bee or Not To Bee,” in The Magazine. He tells us that spring is coming.
Ensconced under the earth and insulated by a blanket of snow, bumblebees lie slumbering for the New England spring. The workers of last year are long gone; the male drones frozen and lost. Only the queens remain, waiting.
For the past few years, I have chased bumblebees from museums to my backyard to the tops of the Green Mountains with biologists and citizen scientists, on a quest to understand their conservation status. Each year in March, with the maple sugaring season in high gear and the snow pack receding, with my close-focusing binoculars hanging nearby and my camera empty with promise, I also wait.
For years I waited for the arrival of migratory songbirds. And then it was for the spring eclosure of butterflies. Now it is for the emergence of queens. Seeing things through a lens leads to certain fascinations.
Each year in the bumblebee kingdom, only the young queen, hatched in the dog days of summer, will carry the colony’s torch through winter to produce the next generation. Everyone else — workers, drones, and the old queen — dies with the onset of fall frost.
During the waning days of late summer and early fall, larvae begin to develop into virgin queens and males rather than the workers that have been hatching all summer. Some colonies will produce up to 100 reproductive individuals, hoping that at least one or two queens will survive to establish a colony in spring.
When male bumblebees emerge from the cocoon, they may spend several days in the hive and drink some of the stored honey. Bumblebees do produce honey, just not the great quantities of their honeybee brethren.
The males soon leave the nest to forage and live on their own, often finding shelter under plant leaves and flowers during inclement weather and at night. You can find them in the cool morning air sitting motionless on sunflowers in the garden. The male bumblebees have one charge in life: stay alive long enough to mate. Each male leaves a chemical attractant along a regular flight path marking his territory.
New queens emerge from the hive a week after the males. Unlike the males, they will leave the nest to forage by day and return for shelter at night. And unlike their sisters, the workers, they do not add any provisions to the nest.
As the days grow shorter, a fertilized queen visits flower after flower, drinking lots of nectar to build body fat and fill her honey stomach. The honey stomach is a small sack that can hold between five-hundredths and two-tenths of a milliliter (A teaspoon holds about five milliliters). Each flower may yield only one thousandth of a milliliter of nectar, causing the queen to visit up to 200 flowers to get her fill.
Not all flowers are alike. Fall flowers like goldenrod and aster, for example, generally yield far less food than jewelweed blossoms. Bumblebees must sustain thoracic temperature at 86° to 95° F. to be able to fly. So when the morning temperatures are cool, it does not pay for them to visit flowers of poor quality, because they burn as much fuel as they gain from foraging. Queens won’t emerge to forage in the cool mornings until the air temperature reaches near 50°.
While the young queens are foraging, they are also detecting the perfume left by a male. If the scent is to their liking, they may land and wait for the male. Mating can last up to an hour and a half, but sperm transfer generally occurs in the first two minutes. Why the long encounter? Males want to make sure the future colony belongs to them. When he is done mating he exudes a gummy sealant that helps to block other males from mating with her.
When the queen has mated, she searches for a good place to burrow into the soil for the long winter wait. Once under ground, usually one to six inches down, the queen somehow knows to avoid the false start of temporary winter thaws.
Finally, in April or early May, when the warmth of the spring sun penetrates her underground home, she emerges. And I follow with my binoculars and camera in hand to witness another year in the life of bumblebees.
Kent McFarland is a senior conservation biologist at the Vermont Center for Ecostudies. He’s seldom far from a pair of binoculars and his camera. When he’s not physically immersed in biodiversity, he is often virtually. When he’s not working, you might find him down at the volunteer fire station.
Please contact Kent about licensing and using his terrific bee photos.
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