Why Do Bumble Bees Bump Against Windows?

“I keep seeing large bumble bees bump against windows of our home. Why do they do that? Will they be hurt?”

Every year I am asked this question! It frequently happens early in the season, typically when new bumble bee queens have emerged and are looking for a suitable nest site.

Why do bees fly against the window?

A main reason is that generally, some bumble bees are attracted to shade when looking for a place to nest.

They will seek out crevices and holes that look as though they may provide shelter. Looking from the outside in, what the bees see is a dark area worth exploring. Unfortunately, this is when bees will bump against the window.

Does it hurt the bee? I can’t be sure, but since I have not heard of bees knocking themselves out as a result, and no reports of dead bees by windows, I assume no lasting damage is caused!

“Bumble bees keep getting trapped in my house”

If you have open windows, then chances are you may get one or two bees flying into the house.

My advice is keep calm – they are not out to sting you on purpose! However, if you are afraid of being stung, by all means wear protective clothing.

Gently place a cup or glass over the bee, and slide a piece of card beneath the glass, and take the bee outside.

If you are allergic to bee stings, then it would be better to allow some-one else to remove the bee for you!

Bumble bees bumping against windows inside a greenhouse

During the warm weather, if you have the greenhouse door open, you may well get bees flying in, attracted by the plants inside. This is good news if you need them to pollinate your tomato plants, but what if you want to help them leave the greenhouse?

My method is to leave the greenhouse door open, and have plants by the door, poking into, but ultimately leading out of the greenhouse. Earlier in the year I had phacelia (irresistible to bees!) and after that, there were mimulus and poppies.

You can always position pots of plants to encourage the bees out of the greenhouse if necessary. It may seem that the flowers would attract bees into the greenhouse in the first place. However, I tend to find that I can leave the bees to find their own way out when I have plants by the door, whereas previously I felt I had to intervene and help the bees find a way out of the greenhouse whenever I saw bees bumping up against the windows!

Bees fly in windows

show/hide words to know

Efficient: doing a job or task without wasting time or energy.

Lift: the force acting in an upward direction that helps animals and objects to fly. more

Pulsation: a beating, throbbing, or vibration that is often repetitive.

Rigid: hard and stiff.

Thorax: in general the part of the body between the neck and waist in humans and the central part of an insects body where the legs and wings are attached. more

What’s All the Buzz—How Do Bees Fly?

Have you ever wondered why you hear bees buzzing? Buzzing is the sound of a bee’s beating wings. Bees have two wings on each side of their body, which are held together with comb-like teeth called hamuli. These teeth allow the two wings to act as one large surface and help the bee create greater lift when flying.

Bees have two sets of wings, one larger outer set and one smaller, inner set. Image by Julia Wilkins.

In each set of bee wings, the large and small wing is connected with hamuli, which are kind of like hooked comb teeth. Click to enlarge.

In order to beat these wings, a bee has muscles that cause its thorax to squeeze in two directions: both up-and-down, and left-and-right. The bee alternates these rhythmic thorax pulsations, kind of like how we breathe, but instead of pulling in air, these pulsations cause the bee’s wings to beat back and forth. This also allows bees to beat their wings very quickly and fly.Honey bees can beat their wings over 230 times per second.

The Science of Bee Flight

This animation shows how a bee moves its wings during flight. See the image below for a step-by-step view of the wing path.

Scientists used to think that a bee’s wings were rigid, making bees kind of like little planes that moved hard wings up and down. But bee wings are fairly small for their body size, so even at 230 beats per second, rigid wings wouldn’t be able to let bees fly. For many years, scientists couldn’t understand how it was possible that bees could fly. But then, using high-quality video that could show the bee wing beats in slow motion, they finally figured it out.

Understanding bee wings was key to figuring out how bees could fly. Their wings are not rigid, but twist and rotate during flight. Bee wings make short, quick sweeping motions front and back, front and back. This motion creates enough lift to make it possible for bees to fly.

The path of a bee’s wings during flight. Click for more detail.

Some other insects have a longer motion from front to back and a slower wing beat. The slower beat makes other insects more efficient, meaning they can get more lift with less work.

So why might bees use an inefficient way of flying? Scientists think that the style of flying bees use lets them carry heavy loads when needed. That ability comes in handy a lot for honey bees, who carry nectar and pollen from flowers back to the nest.

Additional images via Wikimedia Commons. Bee hovering at lavender flower by photophilde.

This myth people keep quoting about how bees shouldn’t be able to fly is scientifically incorrect — here’s why

Bee Movie has quite the cult following. There are numerous YouTube videos devoted to it, such as «The bee movie: but every time there say bee it speeds up.» Someone loves the film so much that they watched it on Netflix 357 times in 2017.

But Bee Movie is also spreading lies.

Here are the opening words to the film:

«According to all known laws of aviation, there is no way that a bee should be able to fly. Its wings are too small to get its fat little body off the ground. The bee, of course, flies anyways. Because bees don’t care what humans think is impossible.»

It’s a nice idea, but in reality bees do not disobey any laws of physics. If they did, bees would be responsible for ripping apart time and space whenever they flew around.

The myth dates back to the 1930s, when the French entomologist August Magnan noted that a bee’s flight should be impossible, because of the haphazard way their wings flapped around. And if bees flew like aeroplanes, he would be correct.

Aeroplanes can fly because of a careful balance of four physical forces: lift, drag, weight, and thrust. The lift force must balance its weight, and thrust must exceed its drag, to make flying possible. Planes use wings for lift and engines for thrust. Drag is reduced thanks to a streamlined shape, and lightweight materials.

The wingspan of a plane is large enough to satisfy the lift equations for flight, so they don’t need to flap. But the small wings of a bee compared to its relatively fat body are not. A regular Boeing 747 plane can also take off at roughly 184 mph, whereas bees do not reach anywhere near that speed.

Due to low speeds, and the high amount of drag when bees flap their wings, it might look like they shouldn’t be able to fly. In reality, they simply fly in a completely different way.

One study from 2005 helped explain the way bees get themselves off the ground. The scientists compared bees to fruit flies, and found that a fruit fly has one eightieth the body size and flaps its wings at a rate of 200 times per second. In comparison, honeybees flap 230 times per second.

This was surprising because smaller insects generally have to flap their wings faster to compensate for decreased aerodynamic performance. To further complicate things, bees are also often carrying pollen and nectar, which sometimes weighs as much as their entire bodies.

In the study, the researchers put bees in a small chamber filled with oxygen and helium, which is less dense than regular air. Bees had to work harder to stay in the air, which allowed the team to observe how they compensated.

They saw that the bees stretched out their wing stroke amplitude, but didn’t adjust the frequency.

«They work like racing cars,» one of the authors of the study, Douglas Altshuler, told Live Science. «Racing cars can reach higher revolutions per minute but enable the driver to go faster in higher gear. But like honeybees, they are inefficient.»

Another study from 2005, by biology professor Michael Dickinson from the University of Washington, also concluded that bees flap their wings back and forth, not up and down. This was previously a big misconception about the way insects fly, and could have originally been what tripped Magnan up in the first place.

An aeroplane’s wing forces air down, which pushes the plane upwards. Insects sweep their wings in a partial spin. Rather than being like a propeller, the angle to the wing creates vortices in the air like small hurricanes. The eyes of these mini-hurricanes have a lower pressure than the air outside, which lifts the bees upwards.

So the next time someone tells you a bee shouldn’t be able to fly, you should inform them that this is merely a myth perpetuated by popular culture. In reality, bees simply create mini-hurricanes wherever they go, which is a lot easier to get your head around.

Hackaday

Jerry Seinfeld launched his career with Bee Movie, an insect-themed animated feature that took the world by storm in 2007. It posed the quandary – that supposedly, according to all known laws of aviation, bees should not be able to fly. Despite this, the bee flies anyway, because bees don’t care what humans think is impossible.

The quote isn’t easily attributed to anyone in particular, but is a cautionary tale about making the wrong assumptions in an engineering context. Yes, if you model a bee using the same maths as an airliner, of course you’ll find that it shouldn’t be able to fly. Its tiny wings can’t possibly generate enough lift to get its body off the ground. But that’s because the assumption is an erroneous one – because bees don’t fly in the same way planes do. Bees flap their wings. But that’s just the beginning. The truth is altogether more complex and interesting!

Flapping Wings and Dynamic Stall

Regular planes have fixed wings that are, for all intents and purposes, relatively rigid. There is some structural flexibility, but from an aerodynamic standpoint, it doesn’t have a significant effect. These wings generate lift when moving through the air at speed, thanks to their airfoil shape. Increase the angle of the wing relative to the airflow, for example, by pitching up the aircraft, and the wing will generate more lift. This angle is called the angle of attack. Increase it too far, and the flow will separate from the wing, and it will stop producing lift entirely. This is called a stall. Without lift, planes fall out of the sky.

Bees, like birds, and many insects, don’t have fixed wings – instead, they flap their wings to generate both propulsion and lift. The wings are flapped in an incredibly complex motion, with the wing rotating throughout the downstroke and upstroke in order to maximise efficiency. The key to creating high lift with a flapping wing is down to a variety of complex fluid mechanisms.

The leading edge vortex, as visualised on a model of a hovering hawkmoth. Note how the leading edge vortex stays attached to the wing on the downstroke from (a) to (b). (van den Berg, Ellington 1997)

The first is the generation of a strong leading edge vortex through a phenomenon known as dynamic stall, or absence of stall. This is where the wing is at an incredibly high angle of attack on the downstroke and upstroke, which causes the airflow over the wing to seperate, generating a large vortex attached to the leading edge of the wing. This vortex remains attached to the wing, thanks to flow features generated along the span of the wing, in much the same way as delta wings work on aircraft. By keeping this vortex attached, the wing is able to generate high lift thanks to the pressure difference across the wing that would otherwise be absent if the vortex were allowed to dissipate.

The second is down to rotational effects. It’s possible to rotate the wing either before changing stroke direction, during change of stroke direction, or after changing stroke direction. When the wing rotates, this motion adds to the circulation in the existing vortexes around the wing. Doing this in advance of a stroke change, the added circulation in the air creates a boost to the lift generated by the wing; doing it after creates a negative lift force. Doing it symmetrically creates both positive and negative lift peaks throughout the full wingbeat. By varying the point of rotation, it’s possible to vary the lift generation on each flap of the wings.

A diagram showing the difference in aerodynamic performance of wings during advanced, symmetrical, and delayed rotation regimes. The black lines represent the wing, with the dot showing the leading edge. The red arrows show the magnitude and direction of the instantaneous forces on the wing. This data was collected with a robotic flapping wing model. (Dickinson, Lehmann & Sane, 1999)

Other complex mechanisms have also been observed in various types of insects and birds, with many species displaying unique and varied flapping techniques. One technique observed in butterflies is that of wing-wake interaction. A wake is a flow regime seen in a fluid behind a moving object; most commonly observed by humans as the changing flow behind a boat travelling through water. This exists for wings in air as well. In wing-wake interaction, the motion of the wing during flapping creates an interaction between the wing’s flow and the wake shed by the previous flapping motion. As the wake in the air consists of fluid moving because of the flapping wings, interacting with this wake to generate more lift allows the insect to recapture some of the energy already expended to improve its efficiency.

Another commonly cited mechanism is the “clap and fling”, where the wings on either side of an insect are clapped together at the top of the upstroke, squeezing out air between them that helps generate thrust, before flinging apart to begin the downstroke. As the wings peel apart, they create a low-pressure zone between them that sucks in air and helps build circulation during the downstroke. However, this method is not used by all species, and only used in certain flight regimes, so is not a critical component of regular flapping wing flight.

Overall, the fluid mechanics behind flapping wing flight is incredibly complex. A basic understanding of fluid mechanics is required even to parse this very simple explainer, let alone truly dive into the topic. Flapping wing flight is still not completely understood, and is an area of ongoing research around the world. One of the reasons for this is the high level of difficulty involved in studying these phenomena.

Particularly with regard to insect flight, the flow regimes are tiny and difficult to visualise. This has led to techniques such as building robotic analogues of insect wing systems at larger scales and moving the wing surfaces through tanks of mineral oil to better see and understand the mechanisms at play. This allows techniques such as dye visualization to be used, giving insights into the complex three-dimensional flow regimes. Other work involves studying birds, which are larger and easier to observe, and running computer models. However, it’s always necessary to directly study the real thing to confirm any theory.

Regardless of the complexity, the old adage that “bees can’t fly” is provably false, and rooted more in making inappropriate engineering assumptions than any major physical paradox. As always, when running simulations, it pays to make sure you’re modelling the right thing at the get-go.