This female American Bumble Bee is a worker. It is her job to gather nectar and pollen. The nectar she stores in her crop. The pollen is mixed with saliva until it makes a sticky ball which she places in the corbicula on her hind legs. The corbiculum is a smooth hollow surrounded by bristles; it is also called the “pollen basket.” By gathering pollen, bumble bees also carry pollen from flower to flower. They are among the world’s best pollinator species. Steven J. Koch Photo.
While watching hummingbirds feeding at desert willow flowers recently, I noticed a large, hairy bee methodically going from flower to flower. It was black with three yellow bands around its abdomen. It was scarcely an inch long, but it was bulky, rather round at its middle. I figured it was a bumble bee.
I watched the bee squeeze itself into a desert willow flower. Only the tip of the abdomen protruded from the petals. It buzzed a bit and wiggled around; I guessed it was gathering pollen and maybe sucking up some of the nectar. Then it proceeded to struggle and make quite a loud buzz or bumbling rumble. I thought it was stuck in the flower. “Should I help it get out?” I wondered. I hesitated. It thrashed about and eventually came free of the flower. I was glad I didn’t have to help it; I remembered that some bumble bees can sting.
Some bumble bees can sting. Did that mean there are different species and some sting, while others do not? Or do only the worker bees sting? Are there “worker” bumble bees? Obviously, there was a lot I needed to find out about bumble bees!
I consulted several publications and the internet. First, I identified the bee I had seen as an American Bumble Bee (Bombus pensylvanicus) from its color patterns. I also discovered a new book, Bumble Bees of North America, published by Princeton University Press just this year. Imagine a whole book on bumble bees! The website even had a video of photos accompanied by music: The Flight of the Bumble Bee, by Rimsky-Korsakov, of course!
Nine species of bumble bee occur in Texas. When I looked at the county range maps for these species, I was shocked to find that none of the species was documented to occur in Bee County. What? No bumble bees in Bee County? That’s just not right! But in all the counties surrounding Bee County, there are records for the American Bumble Bee. Nobody has gotten around to documenting the bee in Bee County yet. I guess that is going to be my job. However, I am not looking forward to capturing a voucher specimen. (Unless, it is a male.)
Using the identification key, I determined that the bumble bee I saw was a worker bee. Queen bumble bees are huge: twice as big as this little worker. Males have yellow faces and more yellow on the abdomen. Males cannot sting either, so if you must grab a bumble bee, grab a male one. Like honeybees, bumble bees are social insects and they have the three castes: workers (females), drones (males), and the colony’s queen (a reproductive female). Bumble bee colonies are smaller than honeybee colonies. Typically, an American Bumble Bee colony has fewer than 200 individuals in it; sometimes as few as fifty. A bumble bee’s life is short. There is a new generation every year. A queen lives for only one year. The other castes live just a few months.
Right now, bumble bees are preparing for winter. The colony produces new queens and males in late summer. The male bumble bees hatch from eggs laid by the worker bees. The new queens can only form from the eggs of a queen. Both new queens and males are forcibly ejected from the colony. They fly around feeding on nectar and pollen. At night, they sleep among the flowers. Eventually they mate (sometimes more than once) and the fertilized queens begin seeking out places to overwinter. The males and workers and the old queen all die in the fall. Only the new queens are capable of going into diapause, a kind of dormancy, for the winter.
Each new queen survives the winter alone in a sheltered spot or in the ground. When she emerges in the spring, she looks for a colony site. An abandoned mouse tunnel, an old bird’s nest in the leaf litter, a rotten log cavity all can serve as a new home. The queen goes out foraging for nectar and pollen in early spring flowers. She brings the food back to the colony site and using wax she secretes from her abdomen, fashions thimble-sized “honey pots.” She fills the pots with regurgitated nectar (it is not real honey) and stashes them in the colony. When she has made and filled several honey pots, she makes a ball of pollen and lays an egg in it. This egg hatches out into a larva that is fed pollen and nectar by the queen. The larva and others like it, develop into worker females which take over the jobs of feeding larvae and caring for the colony. When there are enough workers, the queen “’retires” and spends most of her time laying eggs. By high summer, she seldom goes out to forage. This is why in summer you rarely see the extra large bumble bees, i.e. the colony queens.
Right about now, the cycle starts over. More males are produced and they forage alongside the workers. You can tell the difference between a male and a worker by the presence of pollen sacs on the hind legs of the worker. The hind leg has a smooth, oval indentation surrounded by bristles. This is the corbiculum, or “pollen basket.” The worker bees and queens load pollen in to these corbicula until they have large bulges of yellow or orange on their hind legs. Males lack corbicula so they don’t gather pollen. They just eat and mate. Still, all three castes of bumble bees are superior pollinators for a wide variety of plants.
Within the next week or so, we will begin seeing the queens again as the new ones leave the colonies. These bigger bumble bees along with the smaller males and workers, will be combing the fall-blooming flowers. Watch for all three castes bumbling along among desert willow, crucita, and duranta in your garden. Think about their life cycle, completed within just one year, and be amazed and honored by their presence.
ESSAY BY KAREN L. P. BENSON
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