Friday, July 17, 2015

Fun Friday Facts #114: How Do Bumblebees Fly?

If you’re a person who exists, you’ve heard the urban legend that bumblebees shouldn’t be able to fly. Ignore the empirical evidence presented by thine eyes, plebe, for almighty Science declares that bumblebee flight defies the laws of physics! Those scientists, always with their laws and theories! When will they ever learn!

As you may have guessed, bumblebee flight does not defy the laws of physics. No one is quite sure how this urban legend got started, but its proponents insist that it was birthed from the mind of either a mathematician or an engineer at a party in the 1930s. That this unnamed but truly hard-hitting scientist was probably drunk at the time is conveniently left out of the stories.

Seriously, though, some accounts do attempt to name the scientists responsible for starting the rumor that bumblebee flight is a physical impossibility. The rumor has been pinned on German aerodynamicist Ludwig Prandtl, who lived from 1875 to 1953 and taught at the University of Gottingen. Others blame Swiss aeronautical engineer Jakob Ackeret.

A perhaps more credible theory is that the assertion first appeared in French entomologist Antoine Magnan’s 1934 book, The Flight of Insects. Magnan referenced calculations supposedly made by French mathematician André Sainte-Lague when he made the assertion that the flight of insects – not just bumblebees, but insects in general – should be scientifically impossible. No one knows how bumblebees, specifically, got stuck with the burden of impossible flight, but perhaps it’s just a natural consequence of being so fat and derpy and having such tiny, tiny wings.

Bumblebee in flight by Pahazzard from Wikimedia Commons.

However, Saint-Lague made at least one crucial mistake on the way to concluding that bees can’t fly – he based his calculations on the principles of fixed-wing aerodynamics, which you may recognize as the science of airplane flight. Bumblebees are not planes. Of course, if bumblebees were planes – with rigid, smooth, fixed wings – they wouldn’t be able to fly. Their bodies would be too big and they wouldn’t be able to generate enough lift.

But bumblebees aren’t planes, and they don’t have rigid, fixed wings. Their wings are flexible. Bumblebees don’t glide; they obviously flap their wings. But how does a bumblebee generate enough lift to take flight and stay aloft? Bumblebees’ wings aren’t long enough to generate adequate lift by flapping up and down, the way birds’ wings do. Instead, bumblebees flap their wings back and forth, in a horizontal figure-of-eight motion. That motion creates vortices, described as tiny hurricanes, above the bee’s wings. Because the air pressure is lower in these vortices than in the surrounding air, the bee is able to stay aloft.

How did scientists figure this out? In one experiment, Chinese researcher Lijang Zeng of Tsinghua University and his team strapped tiny mirrors onto bumblebees and then fired lasers at them. I am not even making this up. Somehow, this allowed the scientists to create precise models of natural bee flight that were more accurate than those created in previous experiments, for which scientists were forced to use tethered bees. Tethered bees apparently don’t fly right, for some reason. 

I'll leave it up to you to imagine how they attached the tethers to the bees.