Readers’ wildlife photos

Today we have another photo-and-text story from Athayde Tonhasca Júnior. His narrative is indented, and you can click on the photos to enlarge them

Cleared for take-off

In 1930s Germany, a renowned aerodynamics engineer was having dinner with a biologist when the conversation drifted to the subject of flying bees. The engineer, possibly animated by a sip or two of schnapps, showed the biologist some back-of-the-envelope calculations to prove that bees could not generate sufficient lift to fly. Apparently impressed by his interlocutor’s acumen, the biologist went on to share with his peers the scientific proof that bees can’t fly. The press picked up on the story, and an urban myth was born – although this is only one of a few tales explaining the origin of the widespread belief that scientists have proved that bumblebees can’t fly (nobody knows how bumblebees got involved).

But as bumblebees carry on stubbornly contradicting science by doing what they are supposedly unable to do, one group of people found the explanation for this paradox: creationists. “Of course, our Creator God knows how to make a bumble bee fly, even if the best of modern science can’t figure it out” (Creation Moments, an American creationist broadcaster); “God created all living things, therefore, He knows exactly how to make a bumble bee fly, even when it defies logic, and when even the best of modern science can’t figure this thing out” (The Washington Informer, an American creationist publication).

A flying bumble bee: a miracle in action © marsupium photography, Wikimedia Commons.

Alas, what the anonymous engineer proved to the gullible biologist was that 1930s mathematical models were too crude to explain the flight of a bee. The aerodynamics theories available then were based on observations and experiments with the rigid wings of an aeroplane. Under these models, a bee couldn’t possibly fly however much wing-beat power it mustered; its wings are too small for its body size, and would generate too much drag.

But the flight of a bee is much more complex than an aeroplane’s. Bees’ wings are not stiff structures that flap up and down; they bend, twist and rotate to make quick, arched and sweeping waves forwards and back. The angling of wings and a very high wing-beat frequency create vortices of low pressure under the bee, keeping it aloft. So bees are more similar to crude helicopters than to aeroplanes. Bee aerodynamics have been extensively studied and explained with no need for heavenly input (e.g., Sane, 2003. Journal of Experimental Biology 206: 4191-4208; Altshuler et al., 2005. PNAS 102: 18213-18218).

The flight of a honeybee comprises up-and-down movements, forward-and-backward movements, and torsion (the partial rotary movement of the wing on its long axis). The wing tip describes a long, narrow and slanting figure of eight © Arizona Board of Regents / ASU Ask A Biologist:

Even with these intricate manoeuvres, flying is challenging for a chunky bee such as a bumblebee. Brute force is needed to sort out its weight problem: a bumblebee beats its wings up to 200 times per second. Such tremendous speed is only possible thanks to the bee’s morphology. Unlike birds and bats, bees’ flying muscles are not attached directly to the wings, but to the thorax. Dorsoventral muscles run from the top to the bottom of the thorax, and dorsal-longitudinal muscles run from the front to the back of the thorax (the wing muscles of mayflies, dragonflies and cockroaches have a different configuration). By alternating rhythmic pulsations of these muscles, a bee squeezes and expands its thorax, generating a great deal of energy that is channelled into wing-flapping at mindboggling speeds, akin to vibrations of a bowstring. Watch the whole cycle in slow motion, and the result in real life. [JAC: don’t miss going to these two links!]

A bee’s flying apparatus: the contraction of the longitudinal muscles and relaxation of the vertical muscles expand the thorax upwards and drive the wings downward. The relaxation of the longitudinal muscles and contraction of the vertical muscles push the thorax sideways, driving the wings upward © John R. Meyer & David B. Orr, North Carolina State University.

The buff-tailed bumblebee (Bombus terrestris) – and presumably other bumble bee species – makes its life even more complicated by flapping the left and right wings independently, which is an aerodynamically inefficient, not to mention inelegant, way of travelling (Bomphrey et al., 2009. Experiments in Fluids 46: 811–821). But inefficiency does not stop bumble bees. Some species are capable of migrating hundreds of kilometres (albeit with the help of wind currents); others have been recorded living in montane habitats as high as 5,000 metres, where oxygen levels and temperatures are taxing to most flying creatures. The fittingly named Bombus impetuosus can go further up: males released inside a chamber with an atmosphere rarefied to pressures equivalent to an altitude of 9,000 m (higher than Mount Everest) could sustain flight by simply beating their wings in broader strokes (Dillon & Dudley, 2014. Biology Letters 10: 20130922). Cold and lack of food would prevent such an adventure, but not aerodynamics.

Fly over that mound? Not a problem for B. impetuosus © Rdevany, Wikimedia Commons.

Thanks to their high-energy fuel – nectar – bumblebees can easily fly for several kilometres in search of pollen and more nectar. They can, but prefer not to. Shorter trips are more energy-efficient than long journeys, so bumble bees tend to stick around their nests (50 m to 2 km radius) as long as the surroundings are rewarding, food-wise. Other bees follow a similar pattern. Even small species can go over the 10 km mark, and the orchid bee Euplusia surinamensis seems to hold the record: a marked and released bee found its way home from a distance of 23 km through the jungles of Central America (Janzen, 1971. Science 171: 203-205).

The orchid bee E. surinamensis, a long distance flyer. Art by Dru Drury, 1770. Wikimedia Commons.

 

Bees’ flying distances are usually correlated with body size, but overall they tend to maximise energy gains by keeping foraging expeditions short. This has implications for the management of pollinators’ habitat. As a general rule, based on results from a number of bee species, flower patches are best placed within a few hundred metres of each other to facilitate foraging and reduce the risk of bees running on empty (Zurbuchen et al., 2010. Biological Conservation 143: 669–676).

The flight of a bee is not mysterious or miraculous, but it is a complex and demanding activity. Bees resort to it judiciously for their survival.

The dream of flying: Jack-of-all-trades Tito Livio Burattini (1617-1681) guaranteed that landing his glider Dragon Volant would cause ‘only the most minor injuries’ to the pilot. Supposedly a cat was its first and last passenger (Hart, 1985. The Prehistory of Flight, U. of California Press). Wikimedia Commons.