The life and death of a humble bumblebee
If you have the uncommon luck to come across a bumblebee nest this summer – perhaps in your garden or along a favorite forest trail – you may wonder, “How did this nest get here? I didn’t notice it last year”. The truth is that you didn’t notice it because it probably wasn’t there before; bumblebee nests rarely occur in the same place two years in a row, in part because of the bees’ unique life history. Bumblebees and honey bees are social, but unlike their perennial, more bare bee brethren, a fuzzy bumblebee queen survives for only one year, leaving her regal offspring to overwinter alone and find new digs come spring.
Keen gardeners sometimes find these overwintering queens when they return to yard work in late winter or early spring; bumblebees are found hibernating in compost bins and long-undisturbed flowerpots. Normally triggered by rising temperatures, the queen may emerge from the ground as early as February; her insulating ‘fuzz’ lets her fly in cooler air and lower light levels than any other bee species. This ability to emerge early in spring and flourish late into the fall requires bumblebees to be foraging generalists – able to feed on many different flowering plants.
As the newly emerged queen forages for nectar and pollen to feed herself and her first few offspring, she zigs and zags characteristically low to the ground, looking and smelling for a house to call home. (Whether or not she avoids the attention of birds overhead is a matter of life and death, as robins have been observed catching bumblebees, rubbing their stingers off on branches, and pecking their prey apart.) Our queen is searching for a dry, dark cavity, and depending on her species may prefer to establish her nest underground (for example in a chipmunk’s abandoned burrow), inside a thick tussock of grass, or high up in a tree hollow. Of course, she might end up selecting a cavity that used to belong to another bumblebee colony.
After choosing a nesting hole, the bumblebee queen builds several tiny cups – called "brood cells" – out of wax excreted from special glands, lays her eggs within, and provisions them with pollen and nectar. Her nest looks messy, lacking the distinctive hexagonal blueprint of a honey bee hive. She piles up the brood cells and stays with them, vibrating her body to keep her eggs warm, while nourishing herself on a wax-cup of nectar, aka "honey pot", stored inside the nest. It can take the queen’s eggs up to a month to hatch into larvae and then metamorphose into pupae and finally into female worker bees.
Once she establishes her nest, the queen rarely leaves to forage, instead producing and raising multiple overlapping generations of worker bees throughout the spring and summer. Her nest will produce very little honey – only enough to feed larvae and workers during stints of bad weather. A single worker bee will live for several weeks, constantly foraging, helping raise younger offspring, or guarding and maintaining the nest. You may have found that bumblebee nest when you noticed dead larvae and bees surrounding its opening; worker bees discard these to clean the nest and protect it from disease. The bumblebee queen’s nest may support anywhere from 50 to 400 bees, making it less conspicuous than a honey bee hive, which can house up to 60,000 inhabitants.
Near the end of the summer, the queen stops producing worker bees and begins to produce male bees and new queens, who leave the nest to forage and find mates elsewhere. Our original queen and her workers will all naturally die off. New, mated bumblebee queens may continue foraging heavily into November, and will be the only bumblebees to survive the winter.
To help bumblebees survive for years to come, we need a better grasp on the health of their populations and what needs to be done to sustain them. We are currently raising funds to help complete the assessment of all bumblebee species. Please consider helping us reach this goal. Donate now.