Why Do Flies and Other Insects Hit Windows – ANSWERED!

Flies and other insects normally hit windows because they can’t focus. These insects fly right into closed windows rather than using any opened sides because they can’t distinctly tell colors apart and they normally see images in the form of a blur.

That being said, there’s way more to this question than a simple answer paragraph. So keep reading as there’s some things you’ll learn that will surprise you!

How Do Flies Fly and Operate in Their Natural Habitat?

When it comes to movement, we can say that these insects are highly versatile in their natural habitat. They can move vertically, backward, forward, and hover around.

That’s why it’s quite hard for human beings to effectively catch. we can confidently describe them as acrobatics thanks to these stunts that they keep pulling.

The Structure of the Compound Eyes

When it comes to vision, flies can’t focus. While its eyes are spherical in shape, they are still immobile. It’s their location (the protrusion on the head) is normally what gives it the 360-degree viewing angle. They don’t have the focus like the human eye with pupils that control how much light enters into it.

Compound eyes have thousands of individual visual receptors i.e. ommatidia. Due to a large number of ommatidia, these insects usually end up with a broader field of vision.

It should be noted that each ommatidium is usually thin and long. Besides that, each ommatidium has a lens on the external surface and then tapers to a nerve that’s located in the base of the eye.

When there is light, the ommatidium filters it through its lens, and then it’s processed in the brain via the optic nerve.

The Mosaic Effect

This is the best analogy that we can use to describe the fly’s vision. It involves small images convalesce and as a unit, they represent one visual image.

We can describe this image the way we see a newspaper print. When you move it closer to your eyes, you will only see the letters or numbers that are blurry. That’s what flies see and as a result, they can’t create clearer images.

Lightwave interpretation

Because they have limited color vision, these insects have to rely on light waves. Understand that every color usually has its own frequency wave. However, it should be noted that these insects usually have only two types of receptor cells for colors.

As a result, they can’t effectively distinguish various colors. They can’t even see the red color that is the lowest frequency which the human eyes can see. But because they can effectively see polarized light, they are able to move around.

Note: polarized light is a type of light that has waves that travel in one plane. As human beings, we don’t have the ability to effectively differentiate between unpolarized and polarized light.

The Flicker Effect

This is a motion detection feature that helps them to move around. This is based in the flicker effect and it means that the fly’s field of view usually fires and stops. It’s like turning on and off light in order to get the illusion of motion.

Why Do Flies and Other Insects Hit Windows?

By now, you have definitely witnessed how flies and other bugs normally hit windows. It’s like they don’t normally see where they are going or they are completely blind.

Some of them even hit these surfaces so hard that they end up dying. But why do flies and other insects hit windows? Well, below is an overview that gives details in relation to this.

Large Compound Eyes

Flies have amazingly good complex eyes that feature both simple and compound eyes. Scientifically, the eye structure of flies usually consists of a honeycomb shape. Besides that, the eyes also have more than 8,000 lenses.

This means that they can effectively detect all movements around them as their eyes can rotate through 360 degrees. They can also detect movement in polarized light and UV lights. Furthermore, they possess good color vision.

A study that was done by the Utah Education Network indicates that flies have large compound eyes that allow them to quickly detect any form of movement.

However, one downside of such eyes is that they can’t focus. This means that these insects usually see everything as a blur. Yes, the images are simply blurry and nothing is clear.

As a result, they can easily hit window panes because of their transparent nature. These insects would unknowingly hit themselves to death against your window panes rather than simply fly out via the open half of the window because they can’t spot the difference.

Overall, the downside of compound eyes is that it isn’t effective in determining distance.

This means that flies have to depend on other sensors such as the antennas and legs to determine if there is an object around. And if they are flying, it would be very difficult for them to see windows.

Light Rays

Generally, flies usually use light as the main means of orientation. They heavily depend on the light from the sky in order to navigate. Research studies indicate that houseflies usually move towards sunlight. That’s why you might find them collecting around glass windows and doors.

However, flies that hit windows are most likely disoriented. Windows usually allow UVA rays to pass through them. Meanwhile, they usually block UVB rays. In such a scenario, the fly might get easily affected by these two confusing light signals.

Because of their compound eyes, flies may easily miscalculate the light signals because both of these rays usually come from the sun.

The only difference is that UVB rays are short wave light rays while UVAs are long-wave light rays. Even though they are not visible to human beings, flies can actually see them.


There is some direct correlation between temperatures and when the flies hit glass windows. Generally, we tend to see lots of flies around during spring and summer because of the warm environment that encourages breeding. However, temperature can also influence how flies move around.

Several studies conducted on the fly behavior and physiology simply add to the complexity of what flies normally experience when they come face to face with windows.

It’s common knowledge that these insects are actually very active when there is light. In addition to that, their level of activity usually increases when the light intensity, humidity levels, and temperatures begin to increase as well.

With all these factors around the flies’ environment, the insect is surrounded by several stimulating factors and they definitely can’t handle all of them at once.

While trying to find its way around, it may end up hitting the window because it’s definitely hard to move around while they are very active. So, these insects might end up hitting windows because they are stimulated and very active but they simply don’t know what to do.

Other Environmental Signals

Just like we have stated above, it’s clear that the behavior of these insects is heavily influenced by what’s happening in the surroundings. Factors such as age, sex, and nutritional state also come to play.

However, we shouldn’t forget that the searching activities of flies in relation to the visual stimuli that’s present in the environment.

A study that was done by the University of Groningen indicates that flies usually follow the aroma or odors produced by food. And why would this relate to them hitting windows to their death?

Well, first, it’s clear that these insects can’t tell the difference between closed and open windows. So, they usually try to fly in like everything is simply open.

Secondly, food odors usually emanate through window openings and cracks. So, while they try to move towards the direction of the aroma, they find it hard to navigate through the window panes.

In a hurry to get to the other side where the aroma is coming from, these insects end up hitting themselves to death on the windows.

Note: during cloudy days, flies have more landing power. This is because the sunlight seems to falter more. It’s also important to note that glass windows are things that flies don’t expect to find in their habitats. So, flies can’t possibly tell if they exist because they don’t have natural instincts to detect their existence. They can’t properly perceive a transparent object. It would also be difficult for you to keep walking around as a human being when your vision isn’t capable of seeing certain objects.

How Fast Are Flies Travelling When They Hit the Windows

A common housefly can move at a maximum speed of just five miles per hour. However, it should be noted that its wings can beat more than 20 thousand in just a minute.

While its fly speed may seem to be quite low, try to swat it and you will soon realize that it’s actually faster than you.

Generally, these insects usually see images as a continuous video. This means that they quickly piece together images based on distinct flashes that occur a number of times per second.

While human beings process images with an average flash of 60 per second, flies have 250 flashes per second.

This is quite a higher rate. While, this means that it’s not easy for us to swat them, the fat that flies process images in the form of continuous videos means that it impairs visibility when it comes to transparent objects.

That’s the main reason why they end up hitting windows so hard and end up dying.

What Type of Force Do Flies Exert On Impact?

Are you ready for some physics? Well, the type of force that helps these insects to move around is newton’s third law of motion. If we look at this law then we will realize that nature has some form of symmetry.

It means that forces usually occur in twos or pairs. I.e. if a body A exerts a force on B, B will also react and exert a force back on A. action and reaction are equal and they occur in opposite directions.

When a fly hits the window, it exerts pressure on it. The window, on the other hand, will exert pressure by pushing back. However, the body of flies can’t effectively withstand the force on impact and that’s why they usually end up dying

When Are You Likely to See Flies Hovering Around Your Window?

Well, you can definitely see flies at any time of the year. These are insects that have a short life span so, there are multiple cycles in a year that lead to the breeding of flies constantly.

However, the number of flies usually decreases during fall to winter due to the cold weather.

You are likely to see a higher number of flies in spring and summer because they love warmer environments that allow them to breed and thrive. These insects are also not nocturnal so you are very likely to see them during the day when there is light.

How Can You Effectively Keep Flies off Your Window

When a fly crashes of your windshield, it will definitely leave grime or blood behind. This can be hard to remove and the streaks of dirt can interfere with your visibility.

Well, safety is important while driving, and visibility is a crucial factor. So, what are some of the techniques that you can use to ensure that flies don’t splatter on your window?

Repellent Formulas

There are repellent sprays that have been specifically formulated to stop bugs from settling on the windows. This is usually a waterproof coating that helps to prevent flies that have hit the windows from sticking to the glass.


It’s clear that flies and other insects normally beat themselves to death when they hit windows because they can’t focus. Rather than flying through the open space, these insects don’t have the power to effectively differentiate between open and closed windows. In addition to that, they can’t tell if the window exists in the first place.

While flies might have a huge angle of vision, it doesn’t necessarily mean that they can see objects clearly.

In fact, to them everything is blurry and they have to depend on motion signals and other environmental factors such as odor.

If you want to learn more about various insects, then checkout our site categories, we have a bunch of articles there that are totally worth reading:


Pest Category





That’s it for this article. I hope you enjoyed reading it and if you think it might be useful for someone else then please share it on social media, email or your own website! It really encourages us to write more content and grow the site!

All the best


Steve Foster

Mad about bugs and wanting to publish as many articles as I can to help educate people about these amazing beautiful creatures! For more info check out my about page https://schoolofbugs.com/about-steve-foster/

Recent Content