How Many Eyes Do Flies Have?

Macro sharp and detailed fly compound eye surface.
Komsan Loonprom/Shutterstock.com

Written by Mitchelle Morgan

Published: April 8, 2023

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Catching or swatting flies isn’t easy because their response to danger is instant. Eyesight is critical to their swift reaction.

The structure of individual animal eyes depends on the species type, environmental adaptation, and evolution. Flies’ eyes are different from those of mammals or reptiles. They have a uniqueness lacking in humans and other animals.

Let’s find out how many eyes flies have and how the eyes contribute to a fly’s survival.

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.

How Many Eyes Do Flies Have?

Arthropods have compound eyes, and flies belong in the group. They have two large compound eyes occupying most of the facial surface.

Each eyeball has thousands of lenses, enabling them to see a wider field around them without turning their heads. The number of lenses per eye can range from 150 to 8,000. However, other arthropods, such as dragonflies, have 30,000 lenses in their magnificent compound eyes.

Some families, however, can have additional eyes known as Ocelli, which they use for navigation when flying.

Compound eyes are made of multiple lenses called Ommatidia. Each ommatidium has a light-sensitive receptor that detects shapes and color variation.

The numerous lenses help a fly to have a wider visual range.

Animals that use mimicry – robber fly

Compound eyes are made of multiple lenses called Ommatidia.

How Does The Compound Eye Of A Fly Function?

They have compound eyes made up of tiny, simple eyes called ommatidia. Each ommatidium collects light and transmits visual information to the brain.

Ommatidia concentration in a compound eye varies widely among the species and families. Their vision ability largely depends on the number of ommatidia in the compound eye.

 The higher the number of lenses, the better the vision. Compound eyes can sense movement, so they are well-adapted to detecting danger, prey, or predators.

The eyes also allows them to see ultraviolet light. The ability aids in navigation using UV-reflecting objects, including flower nectar.

Their eyes have many advantages, but they also have some limitations. For example, they cannot form images of stationary objects, so they are way back in line regarding reading or writing.

Nevertheless, the compound eye has evolved to become an efficient and valuable type of eye, meeting the needs of many different insect species.

Fly - Insect, Insect, Flying, Housefly, Fruit

Vision ability in flies largely depends on the number of ommatidia in the compound eye.

How Do Flies’ Eyes Differ From Other Animals’ Eyes?

The eye of a fly is different from other animals’ eyes. It has an amazing structure of its own. Here is why it fairs better than other animals.

  • Their eye is compound, comprised of individual lenses or ommatidia. The lenses enable the eye to capture a broader view than other animals without moving its head.
  • The lenses in the eye allow them to see ultraviolet light.
  • Compound eyes have a higher resolution making them see even fine details missed by other animals’ eyes.
  • Their eye can easily detect movement, enabling the Fly to hunt and avoid predators easily.
  • The eyes do not orbit in their sockets but, unlike in other animals, when reaching broader focal points.

Here is how a fly eye is inferior to that of other animals

  • They do not have eyelids, so they seek underneath leaves or other protected dark places when sleeping.
  • Their eyes do not have pupils. Sadly, that means the compound eyes cannot control the amount of light that enters. Some forms of light can cause damage to their eye, like blue light, as observed in some cases.

The combination of these factors makes flies have the most incredible eyes in zoology.

Horsefly sitting on the human skin

Flies’ eyes do not have pupils. Sadly, that means the compound eyes cannot control the amount of light that enters.

What Are The Benefits Of Flies’ Eyes?

Their eyes have up to four times more light-sensitive cells than a human eye, giving them exceptional visualization.

View Range

The main advantage of compound eye structure is a wider view. It gives them and other Arthropods a comprehensive view of their surrounding without turning their heads.

The combination of the two eyes gives a fly a 360-degree view around it.

Range Of Colors

They can see a broader range of colors, including UV light. The ability is quite handy in courtship and when navigating physical barriers.

Visual Processing

The speed of processing visual information from their eye is higher than humans’ because their brain is organized differently than ours.

Each eye can communicate directly with a fly’s central nervous system triggering a rapid response to changing environment. As a result, they are among some of the problematic prey for predators.

Scientific Study

Their eyes have helped in technology growth through research. Inventors use ideas borrowed from a fly-eye structure to develop more efficient and powerful solar panels. The structure has contributed to the invention of cameras capable of seeing around corners.

Although they have a small eye, its uniqueness inspires significant inventions.

Are All Flies Eyes The Same?

The number of fly species known so far is one hundred and twenty thousand plus, which means the variety of eyes among the species is wide. Even the species referred to as ‘Blind Flies’ have eyes. The number of eyes on an individual among flies is 2 or 5.

Here are a few species, their number of eyes, and their structural type.

House Flies

isolated housefly

A

House fly

also has three extra simple eyes centrally between the two prominent eyes.

They have two prominent compound eyes composed of 3,000 to 6,000 tiny simple eyes (lenses) working together to make one visual masterpiece.

A House fly also has three extra simple eyes centrally between the two prominent eyes. The three ocelli, as they are known, help a housefly navigate when flying.

Horse Flies

Horsefly sitting on a branch.

Horseflies only have two large compound eyes.

Unlike common house flies, horse flies lack the ocelli. They only have two large compound eyes. The horsefly eyes are good when determining gender.

On close observation, females have a thin black separator between the eyes. On the other hand, male eyes seem to touch each other.

Fruit Flies

Although most flies from the same species share a standard eye color,

fruit flies

have different eye colors.

These tiny flies have two prominent compound eyes. Each eye of a fruit fly is composed of 750 ommatidia.

Although most from the same species share a standard eye color, fruit flies have different eye colors. Their eyes come in either white, red, or black colors.

Blue Bottle Flies

Bluebottle blowfly

Bluebottle flies help the forensic investigation by determining the time of death using the stage of the laid eggs on the corpse.

The Calliphora vomitoria are easily identifiable by their metallic blue color. Bluebottle flies help the forensic investigation by determining the time of death using the stage of the laid eggs on the corpse.

They have two compound eyes, with each carrying a stunning 8,000 lenses.

Crane Flies

Crane fly

Crane flies are harmless and have no venom.

The species is smaller compared to fruit flies. They have only two eyes without the additional ocelli. As most people say, Crane flies are harmless and have no venom.


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About the Author

Mitchelle is a content writer who loves nature. She loves writing about animals and plants. In her free time, she enjoys hiking and going for nature walks.

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