by Whit Gibbons

September 1, 2003

Q. We would like to get some information about bumblebees, these creatures that appear in our backyard as a buzzing cloud of yellow and black. We sit each summer day among hundreds of them that blatantly pilfer the pollen from our many flowers, and it just recently dawned on us that we know birds, hummingbirds, bees, and quite a bit about butterflies, but our knowledge concerning the bumblebee is woefully lacking. Will you help us, please?

The general question was followed by a list of several specific questions such as "Where do they nest? Is it a hive? Do they make honey? What is the purpose of their pollen gathering? Does the normal bumblebee mate, or is that privilege for the hierarchy? Do they sting? Do they have a natural enemy?"

A. Bumblebees, with their rounded, robust bodies, remind me of linebackers that play for a team whose school colors are black and yellow. They are highly watchable creatures to have around a yard. Most bumblebees, of which there are more than 200 species worldwide and 50 in North America, are social insects that live in a nest they build, often in an abandoned mouse nest. I have a bumblebee nest in my yard that is in a bird box that had been the home of flying squirrels this past winter and spring. Like their close relatives the honeybees, bumblebee colonies have a queen. The queen is recognizably larger than the worker bees, all of which are female. Queen bumblebees apparently will sometimes leave the nest to forage like the worker bees. Male bumblebees are known as drones, and their sole purpose is for mating.

Like some of the other social bees and wasps, bumblebees will sting, but only if threatened or provoked, such as when the nest is disturbed. Drones have no stingers and they do not gather pollen like the workers. Most bumblebees are extremely benign, especially when compared to yellow jackets or hornets, which seem to protect their nests with a vengeance. I have never heard of a bumblebee stinging anyone who simply stood and watched one gather pollen on flowers, although they might sting anyone that disturbs a nest and stays to have a closer look.

Honeybees and bumblebees are attracted to flowers to get the sweet-smelling nectar and pollen. During the nectar-gathering process, insects such as bees also transfer pollen from one flower to another, serving an essential role in pollination, a requirement for some plants to successfully produce fruits and seeds. Nectar is returned to the nest by the bee, allowed to dry to a certain level, and then in a complex process that involves bee saliva and special enzymes, is eventually converted to honey. Honey is used to feed members of the colony. Bumblebees produce honey but never in the quantities found in honeybee hives. Bears probably spend little time looking for bumblebee nests to raid.

Even in the southern United States, most bumblebees do not last through the winter, except for young queens that emerge from the nest and mate with drones from other colonies. A future colony queen finds a safe place such as underground or in a tree hole to hibernate through the winter. In the spring she seeks out a site for the nest, where she lays eggs to begin a new colony. The queen can control the sex of her young and early in the season produces only infertile females, the workers. The queen gathers nectar and pollen to feed the first of the developing larvae and pupae, which begin their role as worker bees in taking care of the nest and the young that are produced later.

As far as natural enemies, adult bumblebees probably have few because most predators would prefer not to risk being stung for such a small meal. Ironically, one of the greatest threats to bumblebee colonies in some areas is another kind of bumblebee that is not social. These are nest parasites, sometimes even killing the queen of the colony, laying eggs, and having their own developing young fed by the bumblebees of the colony.

I enjoyed the bumblebee questions. I like to see people become aware that we are surrounded by ecological mysteries and intrigue in the everyday wildlife around us.

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