Why so many dead bumble bees?

Several of you have reported seeing many dead bumble bees on flowers, patios, or lying on the ground. This type of observation pleases me no end. It gives me hope to see so many people noticing wild bees and wondering about them.

As it happens, it is completely normal to see lots of dead bumble bees at this time of year. Unlike honey bees, most bumble bee colonies die at the onset of winter. Some colonies in warm climates may survive the winter, but as a general rule, a bumble bee colony lasts for only one season.

A colony starts with one bee

A bumble bee colony starts in the spring with a single mated queen. This queen hibernated all winter in a cozy protected spot, most often a narrow hole in the ground not much bigger than the bee herself. She survived on fat stored in her body, much like a bear or a hedgehog. You can often see these bumbles in the spring, remarkable for their ungainly size.

When the weather warms in spring, the queen feeds on the nectar of early flowers and cruises the countryside looking for a place to build her nest. The queens of most species choose an underground cavity—perhaps an abandoned rodent hole—as a shelter. In that hole, she begins the process of storing a little nectar, and building a small wax nest for her first batch of young workers.

Once the initial nest is fashioned from secreted wax, and tiny nectar pots are built and filled, the queen sits on her eggs very much like a hen. She keeps the brood warm with her body and drinks from her nectar pots until the young worker bees emerge from their cells.

The chores are turned over to workers

The queen works hard in the early spring, doing all the chores by herself. However, once the first workers emerge, she forages less and less. The labor-intensive jobs of brood rearing, foraging, and colony defense are turned over to her offspring, and she gets down to the business of egg laying. For most of the spring and summer this queen will lay eggs that produce nothing but more female workers.

Because of this system, nearly all the bumble bees you see in the spring and summer are workers. Like honey bees, they ply the flowers for both nectar and pollen, transporting the pollen back to their nests in baskets built into their rear legs.

In general, bumble bees have more size variability than honey bees. While all the honey bee workers in a colony are pretty much the same size, worker bumble bees come in a range of sizes. However, the smallest bumbles spend their entire lives in the nest, acting as nurses. It is only the larger workers that go out and do the foraging. Most of us never see the tiniest house-bound bumble bees.

Queens and males come later

Late in the summer the queen adds to the colony by producing both male bees and virgin queens. If you are observant, you can easily see the changes in your garden. The first thing you might notice is some huge bumble bees and an assortment of very small bumble bees, sometimes on the same flower. As you might guess, the large ones are queens. The small ones are males.

But wait. You never see honey bee queens and drones perusing the blooms, do you? So what are these bumbles doing out on the flowers?

Male bumbles have no home

The males spend their time trying to mate. Many males compete for this honor, but only a few get lucky. The rest of the time, they can be seen in the flowers, drinking nectar for quick energy. As it happens, they also sleep in the flowers because once they leave the nest they are not allowed back in.

Some people mention that these autumn bumble bees often look wet, lethargic, or dead. All of these may be true. The males don’t live very long, and after mating—or attempting to mate—they spend most of their time eating and sleeping. During the cool nights they get wet with dew and stiff with cold. Sometimes they warm up the next morning and live another day, or sometimes they get eaten, or simply die.

Queens fatten up for winter

The queens though, lead a different kind of life. During the fall months the newly-mated queens gorge on nectar and pollen, fattening up for winter. The more fat they can store, the better chance they have of making it through the cold months ahead. Once she is ready, a queen will go and find a nice protected hole where she can hibernate until spring.

Sometimes in the fall you will see a fat queen next to tiny male. Although they forage side-by-side, the difference in size is striking. By evening, however, you might notice dead males adhering to flowers, or dropping into the grass where they are quickly eaten by something else. In contrast, the queens are nowhere in sight, having flown back to the nest for protection.

The colony dies as winter sets in

Back in the colony, life is winding down. One by one, the newly-mated queens leave the nest to begin hibernation. The old queen slows her egg production and eventually dies. The workers die as well. The first hard freeze finishes off all the remaining bees except for the hibernating queens. As we go into winter, the once busy colony is but a memory.

Rusty
Honey Bee Suite