Can Flies See in the Dark?

Written by Angie Menjivar
Updated: May 15, 2023
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Their buzzing is a nuisance, but flies have a whole world of their own. You mostly see them during the day but what do they do when the sun goes down? Can flies see in the dark? Let’s find out!

Can Flies See in the Dark?

When we refer to flies, we’re not just referring to specific ones like drain flies, house flies, or fruit flies. There are well over 100,000 types of flies but they share many characteristics in common. They all have adaptable heads in which there are large compound eyes. They generally prefer warm environments, which is why you see them most often during the summer season. During the day, they’re out and about searching for food, and when the sun goes down, they usually retreat.

Flies can see in the dark. A fly’s eyes adjust to dark conditions and because they have compound eyes, they can focus on any incoming sources of light to make sense of the images they see. This is why they are so effortlessly evasive when you take the fly swatter out. It’s as if they’re reading your mind, knowing where you’re about to swat next so they can get out of the way and survive. But it’s not just about the compound eyes. It’s also about the neural strategy they naturally employ.

How Does a Fly’s Vision Work?

Portrait of a fly on a twig. Eyes to eyes. Macrophotography of an insect fly in its natural environment.

Each eyeball in a fly has thousands of lenses, enabling them to see a wider field around them without turning their heads.

©Videocorpus/Shutterstock.com

Your eyes collect light through a single lens. With flies, there’s more to the story. Despite them having a tiny brain (about one million times smaller than yours), they have multiple lenses that communicate to their photoreceptors. All of this light sensing makes for a different visual experience (and frankly, changes how they experience reality). While their brains are tinier but still house more lenses, they are also limited by how miniature they are. Their perception is low resolution, meaning the clarity with which you see doesn’t compare to a fly’s blurrier vision.

Even though it seems like a weakness, for their purposes it’s a strength. For you, with every second, you can perceive right around 60 light flashes. Anything faster and you don’t notice fluctuations. It all appears steady (except when it’s peripheral). Some flies can see up to 250 light flashes per second. Basically, they’re living in a slide show world while you’re living in a streaming movie world. When the light is dim, they’re not as adept but don’t think you can be more effective at swatting them in the dark. You’re not so adept then either.  

The Neural Component

When it’s dark, flies can see but their vision shifts. It slows. When you make your way from the bedroom to the bathroom, you know to move slowly. Your vision changes and you take longer to make sense of things, even in a familiar environment. It’s blurry, shadows play tricks, and it’s harder for you to figure out your surroundings. For an insect, darkness does a lot of the same. It’d be great if they could change out lenses the way photographers do to ensure a stunning photo when the light is low, but they’re limited.

For flies, it’s all about summation. Summation refers to how a fly combines the images it sees to make sense of what it’s looking at. This is the neural strategy they employ and though they don’t exactly have night vision, it does allow them to put images together even when there are low light levels. They need photons to help them understand their environment and they’re extra slow in the dark as they wait for the static images to come together and form a whole picture.

Tachinid fly

Flies follow a circadian rhythm that dictates when they’re active during the day and when it’s time to rest and recover.

©iStock.com/Mauricio Acosta

Where Do Flies Go At Night?

Flies like daylight. They like warmth. Most often, they’re out enjoying the day when the sun is out. When nighttime rolls around, they move into a time of rest. They can’t exactly thrive when the weather is cool because their bodies reflect outer temperatures. Though they’re energetic during the day, at night, they get tired. They find a location that allows them to rest safely and wait until morning to emerge yet again with the sun. Sometimes, their resting spots include the spaces under fallen leaves, and other times, they opt for a tree’s trunk or branches. They’re flexible on this end, making nearly any spot their accommodation for the night.

They don’t just take a quick stopover either. They sleep just like you! They follow a circadian rhythm that dictates when they’re active during the day and when it’s time to rest and recover. Despite this, they may take a nap here and there during the day as needed. It’s like those days when you sneak out to your car (or wish you could take a spot under your desk) to get a few minutes of rest before continuing on with your day!

The photo featured at the top of this post is © Eric Isselee/Shutterstock.com


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About the Author

Angie Menjivar is a writer at A-Z-Animals primarily covering pets, wildlife, and the human spirit. She has 14 years of experience, holds a Bachelor's degree in psychology, and continues her studies into human behavior, working as a copywriter in the mental health space. She resides in North Carolina, where she's fallen in love with thunderstorms and uses them as an excuse to get extra cuddles from her three cats.

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