Flight of the bumble bee generating a lot of buzz

I WAS recently listening to The Flight of the Bumble Bee, composed by Nikolai Rimski-Korsakov, which reminded me of the oft-repeated riddle – how can the bumble bee fly since aerodynamic analysis shows that this cannot be possible?

I searched the recent literature on this question to discover that the riddle has been solved. A UCC biochemistry colleague, Prof Jim Heffron, also told me about a clever biochemical trick that the bumble bee uses that is essential for its flight.

Bumble bees are important in agriculture as crop pollinators because they can pollinate species of plants that other bees cannot using a technique known as buzz pollination. For example, they are often used in greenhouse tomato pollination because the frequency of their buzzing is very efficient at releasing tomato pollen. Bumble bees are endangered in many developed countries because of habitat destruction and damage from pesticides. Nineteen species of native bumble bee were long recognised in Great Britain but only six remain widespread today.

The wings of the bumble bee are attached to the thorax (the part of the body between the head and the abdomen). Complex contractions of muscles in the thorax changes its shape causing the attached wings to beat rapidly (up to 240 beats per second)

The origin of the claim that bumble bees should be incapable of flight is uncertain. The French entomologist Antoine Magnan is often quoted from his 1934 book Le Vol des Insectes: "I applied the laws of air resistance to insects, and I arrived . . . at the conclusion that their flight is impossible". Such deductions, derived from aerodynamic theory of the early 20th century, claimed that the wings of the bumble bee are too small to create sufficient lift.

Scientists now use relatively simple models to understand how insect wings interact with air to generate lift. Richard Bomphrey, Graham Taylor and Adrian Thomas published an elegant paper in Experiments in Fluidsin May 2009 (another article appeared in Science, September 18th, 2009). The researchers induced bumble bees to fly from their hive down a smoky wind tunnel to collect pollen from freshly cut flowers at the other end. They used high-speed cameras to film vortices in the air and reveal the airflow over the flapping wings.

Bumble bee flight is surprisingly inefficient compared to other flying insects and is achieved largely by “a brute force approach powered by a huge thorax and fuelled by energy-rich nectar”.

Understanding the flight of the bees may help engineers to build insect-sized flying robots. You cannot simply shrink an aircraft wing down to insect-wing size and expect it to work, because the aerodynamics are different.

Bees cannot fly when the temperature of the thorax falls below 30 degrees. But the bumble bee can fly in winds as cold as 10 degrees because it has developed a neat trick to generate heat.

Energy is generated in the body by “burning” energy-rich glucose, ie by chemically breaking down glucose in a long sequence of steps, gradually releasing the energy of the glucose and storing it in the form of an energy-rich biochemical called ATP. The energy of ATP is then harnessed by breaking it down and coupling its breakdown (which releases its energy) to power useful work (such as contracting muscle).

The bumble bee has evolved a heat-generating mechanism whereby, at one point in the long chain of reaction through which it breaks down glucose, it breaks down ATP without coupling the energy released to do any useful work. This process is called a “futile cycle” and the energy is simply released from the ATP as heat. This heat maintains the temperature of the thorax at 30 degrees.

Now that bumble bee flight is understood scientifically, creationists can no longer needle scientists with the taunt that some things in nature are mysteries beyond scientific explanation and explicable only by invoking divine intervention. It would be deliciously odd if God had decided to reveal himself/herself through the flight of the bumble bee!

William Reville is public awareness of science officer and a professor in the biochemistry department at UCC. See understandingscience.ucc.ie