Bumblebees & Old Maids

Farmgirl Confidential

“The number of bumblebees in any district depends to a great extent upon the number of ‘old maids’ that reside there.” This was an observation made by Darwin and later expounded upon by Thomas Henry Huxley, another eminent English biologist. Huxley also pointed out that the success of the British Empire was attributed to these old maids.

Not too many insects could be referred to as cute and charismatic, except, perhaps, the buzzing, plump, and fuzzy bumblebee. Early to rise out of its winter slumber and the first on the job, the queen bumblebee is building her nest before most bees are on the fly. This is because bumblebees are better able to function in colder temperatures than other bees, as they are equipped with a “shivering” response that warms their bodies, a brilliant fur coat and an insulated home.

Many species of bumblebees nest underground in old field mouse holes. Since they’re not equipped very well for nest making, a ready made burrow fits the bill nicely, except for one problem: mice tend to destroy the nest and eat the honeycombs and brood chambers, leaving the bumblebee colony in shambles.

Colonies do not overwinter and each year the solitary queen comes out of diapause (winter slumber) and must seek out a new nesting spot to create her colony. She works alone, as all of last year’s workers and drones have died off. Once a nesting spot is chosen, she builds wax cells in which to lay her eggs that were fertilized the previous year. The eggs that hatch develop into female workers that eventually help in the care of the young. The male bees (drones) are forcibly driven out of the hive and may be the bees you see at dusk, clinging to a flower or leaf, sleeping where the night catches them.

It takes a lot of energy to start all this, and the queen has to find a proper building site located near early blooming flowers to collect energy-rich nectar. The queen tends to visit the same patch of flowers daily, and, although she seeks out a new nesting spot each year, it may be near last year’s site and remembered prime forage areas.

Many bumblebee species specialize in particular types of blooms. In the first edition of On the Origin of Species by Charles Darwin (1859) he describes how essential bumblebees are for the pollination of plants and specifically the red clover (Trifolium pratense). This, he explains, is because of its unique ability to reach the nectar, which eludes other bees, with its extra long tongue. Although honeybees prefer open flowers, most bumblebee species collect nectar from flowers that are tubular. Along with red clover, a few of the bumblebee’s other favorites include thistles, coneflowers, our native butterfly weed (Asclepias tuberosa), sunflowers and lavender.

A bumblebee nest is not organized into hexagonal combs like that of a honeybee. Instead, the cells, like tiny amphorae, are clustered together untidily. Their colonies are small, with 50 to 400 bees, and since the colony doesn’t overwinter there is no need to stockpile food, hence the bumblebee does not produce an abundance of honey for us to harvest.

As the bees search for food to feed the young brood, they remove pollen from flowers, both deliberately and incidentally. Their furry little bodies can’t but help transfer pollen by accident, fertilizing flowers as they go. In queens and workers the pollen is purposely groomed into pollen baskets on the hind legs (made by the same wax used in nest building) where it can be seen as bulging orange masses that may contain as many as a million pollen grains. Male bumblebees do not purposively collect pollen or have pollen “baskets”.

Bumblebees are also capable of a phenomenon called “buzz pollination” in which they dislodge pollen from the flower anthers with the vibration of their beating wings. Bumblebees are important pollinators of both wildflowers and row crops, and although not used for commercial honey making they are particularly useful in the pollination of commercial greenhouse tomatoes by this method.

Speaking of buzz pollination, the old belief that bumblebees can’t fly has no merit, obviously. There is, however, a direct correlation as to why we associate buzzing with bumblebees with the truth behind why they actually can fly. This early, false theory suggested that the bumblebee’s wings were too small to create lift, particularly when attached to such a stout insect. These calculations were made using the aerodynamic theory of 1918, just 15 years after the Wright brothers made the first powered flight. Since then, scientists have made huge advances in understanding the theory behind aerodynamic lift.

One set of accounts suggests that the “bumblebees can’t fly” story first surfaced in Germany in the 1930s during a dinner table conversation between a prominent aerodynamicist and a biologist and a “back of a napkin” calculation. (Other accounts associate the story with students of physicist Ludwig Prandtl (1875–1953) of the University of Gottingen in Germany and still another identifies the researcher who did the calculation as Swiss gas dynamicist Jacob Ackeret (1898–1981). Its all still “up in the air” as to who actually made the napkin calculation.

At any rate bumblebees do fly, but if an airplane were built the same way, it would never get off the ground. It has now been realized that bees aren’t like airplanes, they’re like helicopters. Their wings work on the same principle as helicopter blades, using “reverse pitch”, explained by modern aerodynamics as a moving airfoil which generates a lot more lift than a stationary one. The mechanics behind this discovery is quite amazing. Brute force rather than aerodynamic efficiency is the key to bumblebee flight, since a bee must beat its wings roughly 200 beats per second, which is 10 or 20 times the firing rate of the bee’s nervous system. The trick, apparently, as explained in layman terms by Cecil Adams (Adams is a storehouse of human knowledge), is that “the bee’s wing muscles don’t expand and contract so much as vibrate, (buzz, buzz) like a rubber band. A nerve impulse comes along and twangs the muscle, much as you might pluck a guitar string, and it vibrates the wing up and down a few times until the next impulse comes along.” So there we go, buzz, buzz, buzz!

There are over 250 bumblebee species known worldwide. The largest is Bombus dahlbomii of Chile, which can grow up to about an inch and a half long. Described as “flying mice” or the “monstrous fluffy ginger beast”—can you imagine the sound of that flying by!

Darwin was determined in explaining “how plants and animals, most remote in the scale of nature, are bound together by a web of complex relations” as he wrote in On the Origin of Species. He continued, “I have reason to believe that humble-bees [as they were called during Darwin’s time] are indispensable to the fertilization of the heartsease (Viola tricolor), for other bees do not visit this flower.” He went on to suggest that it is quite credible that the presence of bumblebees in large numbers in a district might determine the types of flowers in that district as well.

“From experiments which I have tried, I have found that the visits of bees, if not indispensable, are at least highly beneficial to the fertilization of our clovers; but humble-bees alone visit the common red clover”, and to this fact both Huxley and Darwin based their belief that for the well being of the bumblebee old maids were indispensable.

Bumblebee species are declining throughout the world due to a number of factors, including habitat loss caused by land-use change, the use of agrochemicals, and pathogens. Another major impact on bumblebees was caused by the mechanization of agriculture and also population growth, accelerating the need for crop production. Small farms depended on horses and oxen to pull plows and carts. The work animals were fed on clover and hay, both of which were permanently grown on a typical farm. Little artificial fertilizer was used then. A typical farm provided flowering clover and flower-rich meadows that supported large bumblebee populations. Mechanization ended the need for these animals after World War II and the need for the great quantities of clover. The use of artificial fertilizers encouraged the growth of taller grasses, outcompeting the meadow flowers. As crops began to use up more free space and wild lands disappeared, wild pollinators like the bumblebees drastically decreased in numbers.

So who are these old maids that saved not only the bumblebee, but the British empire as well? Well, again quoting Darwin from On the Origin of Species, “The number of humble-bees in any district depends in a great measure upon the number of field-mice, which destroy their combs and nests. Now the number of mice is largely dependent, as every one knows, on the number of cats. Near villages and small towns I have found the nests of humble-bees more numerous than elsewhere, which I attribute to the number of cats that destroy the mice.” Continuing that, Huxley went on to expand this observation, pointing out that, “old maids keep cats and cats eat the mice that destroy the bumblebee nests.” So there it is in a nutshell!

Huxley also went on to declare that “the success of the British Empire was attributed to old maids as well since British soldiers were fed roast beef and cattle eat red clover, red clover is solely pollinated by bumble bees. The cats eat the mice who prey on the honey and old maids keep cats concluding that the continuation of the British Empire was thus dependent on its population of old maids.”

In North America you can join Bumblebee Watch to help endangered species of bumblebees. Leaving small areas undisturbed on your property for nest building, and planting flowers and fruit trees are essential in maintaining a healthy bumblebee population.