HERE IN THE Bay Area, we often enjoy spring-like weather while there are still many more weeks of winter ahead, offering great opportunities for outdoor exploration. Whether you step out into your own back yard, a nearby park, or a remote ridge, you are likely to encounter queen bumblebees going about their business.

In our area, bumblebees are active from late winter through mid autumn. The dense fur coat and large size of these bees help to keep them warm, allowing them to forage in cool climates where other pollinators can't get warm enough to fly. This adaptation serves them well in places where summer fog (and the generally cool coastal climate) provides many days where a fur coat comes in handy. For the same reason, bumblebees predominate at higher altitudes and latitudes.

During the warm days of late winter, queen bumblebees emerge from their hiding places and begin to seek out the few flowers in bloom. Manzanita, shooting stars and a few other species come into bloom earlier than most others; these plants depend on bumblebees as pollinators. As soon as the queen finds enough flowers blooming, she seeks out a nest site (usually in an abandoned rodent burrow) where she will start her own colony.

Once a suitable nest site is located, the queen builds a wax "pot" into which she deposits honey (which she makes from nectar). She also makes a ball of pollen mixed with nectar and saliva (called bee bread) on which she lays some eggs. When the eggs hatch, they feed on the bee bread. After two to three weeks, the larvae stop growing, and they become pupae. During pupation, they are transformed into winged adult workers, all sterile females.

The first brood usually consists of about six workers that are much smaller than those produced later in the season. As soon as these first workers are mature, they take over the foraging duties, and the queen will never again leave the nest. For the rest of the spring and summer, the queen lays eggs and tends to the growing larvae as her workers fly to and from the nest gathering nectar and pollen. By midsummer, a single colony may have 200 workers, but colony size is highly variable.

Bumblebees visit a variety of flowers. They have long tongues, so they are able to get nectar from sources that are unavailable to other bees. Bumblebees also have a technique for collecting pollen called "buzz pollination." They forage on many flowers that cannot be exploited by other insects. These flowers tend to hang with the opening facing downward.

When a bumblebee lands on one of these flowers she holds it tightly with her legs and vibrates her wing muscles. These vibrations are transmitted into the flower, causing the pollen to be shaken loose, which falls on the hairy bee's body. The next time you see a bumblebee visiting a plant with upside down flowers, listen to the peculiar buzz that is emitted each time she pauses.

At summer's end, the queen lays eggs that will develop into queens and males. Once they are mature, they leave the nest, and mating takes place. The old queen, the workers and the males all die before autumn. The new queens go find a hiding place where they will wait until the first warm days of the new year bring forth our pre-spring bloom.