Frogs Eyes: 8 Things to Know

Frustrated Spending Hours Preparing Lessons for Your Elementary Students?

Get our 42 lesson plans and a complete video course to help you provide your students factually correct, engaging lessons so you can spend less time preparing and more time teaching.

Have you ever looked at a frog’s eyes up close? They are incredible! They look like tiny planets full of speckles, color and depth.

Frog eyes have horizontal or vertical pupils, can see in color, bulge out to sit above water, and provide frogs almost 360° day and night vision. Frogs eyes also have three eyelids and use their eyes to swallow their food.

This article is about incredible facts you may not know about frogs eyes. Let’s have a look at how frogs have adapted their vision to their environment in order to survive and thrive.

1. Frog Eyes Bulge Out to Sit Above Water

Frogs eyes sit on the tops and sides of their head which is a wonderful adaptation for their survival based on their primary reproductive environment: water.

Frogs have eyes perfectly adapted to their environment as they sit above the water, allowing aquatic frogs to comfortably spend hours with their bodies submerged while they breathe, drink, and hide from predators.

Drawing of what a frog would look like if its eyes did not bulge

Frogs breathe in water, and just imagine if a frog’s eyes did not bulge out. Aquatic frogs would be sitting in water with their eyes submerged, and since they cannot see well underwater, and have many terrestrial and aerial predators, non-bulging eyes would not be helpful for their survival. 

Having eyes on top of their head allows frogs to be able to see what is around them while they sit with their bodies underwater. You can think of it like a snorkel that allows divers to breathe, or the periscope that sticks out of water to allow submarines to see above the surface while remaining below it.

2. Frogs Can See Almost 360° Around Them

Frogs have almost a 360° field of vision allowing them to see upwards and backwards. Frogs can therefore sit in water with a detailed view of what is going on above, below, and around them to spot food or predators.

Another advantage of having their eyes on top of their heads is that this anatomical configuration provides frogs with almost a 360° field of vision. This is key for them to be able to spot predators in the water with them, on land, or in the sky above them. This field of vision also allows frogs to see prey they can eat.

Compared to humans that have approximately 180° field of vision, frogs have a much wider field of view at 360° and can see much more of what is going on above, around and behind them. This is also very practical since frogs cannot turn their heads (they have no neck). 

Here are differences and similarities between frogs eyes and humans eyes:

Frog EyesHuman Eyes
Eyelids32
Field of Vision360°180°
Night VisionYesNo
Nictitating MembraneYesNo
See in ColorYesYes
Bifocal VisionYesYes

Let’s have a closer look at what kinds of eyelids frogs have in the next section since this very much differs from humans.

3. Frogs Have Three Eyelids: Nictitating Membrane

Frogs have three eyelids: an upper eyelid, a lower eyelid, and a third eyelid called a nictitating membrane. The upper eyelid is used for blinking to keep eyes moist, the bottom eyelid does not move, and the nictitating membrane is used for swimming, camouflage, hibernation and sleeping.

Frogs close their third eyelid called the nictitating membrane during sleep in order to keep their eyes moist and to hide from predators. This membrane is partially transparent allowing frogs to detect movement if necessary.

The nictitating membrane is partially transparent and plays a key role in helping frogs swim. Thanks to this third eyelid, frogs’ eyes can be protected from loam, debris, and decaying plants while they swim in the water. However, the nictitating membrane impairs a frog’s vision so they do not see very well underwater.

A frog’s third eyelid also helps them camouflage, hibernate, and sleep. Frogs use their nictitating membrane to hide from predators and camouflage because light could reflect in their eyes and give their location away. During hibernation and while frogs sleep, this membrane helps protect the frog’s eyes while keeping them moist.

Frogs can blink using their upper eyelid or their nictitating membrane and generally do so to to moisten their eyes like many other animals similarly do in the wild.

4. Frogs Use Their Eyes to Swallow Food

Frogs also use their eyes and nictitating membranes to swallow food by sucking their eyes down into the roof of their mouth after having caught prey. Frogs eat live prey that they catch off guard, swallow whole, and suffocate in their stomachs so they use their eyes to push the prey down their esophagus.

Frogs will close their eyes using their nictitating membrane after they catch their prey to help them swallow their food. Frogs are not the only ones that have this third eyelid as it is very common in domestic pets like cats and dogs, as well as diving animals like crocodiles, beavers and sealions. But frogs are one of the rare species that swallow using their eyes.

Enjoyed this video? 🙂 Subscribe to our YouTube channel for more!

I used to watch my toad do this as a kid. I had what I called a “free range” toad that lived in our backyard and I enjoyed feeding it potato bugs. I would drop it in front of a bug and watch it see the prey, turn its body towards it, suck it up, and swallow it, pushing it down by closing its eyes. It would also wipe its face after it was done!

5. Frogs Are Better at Seeing Far Objects 

Frogs see objects that are further away from them better than objects that are up close. Frogs are especially sensitive to movement and will generally approach an object if it believes it is prey, or will escape if it believes it is vulnerable to a predator.

Frogs spend most of their time observing what is around them making one of two decisions:

  1. Can I Eat This?
  2. Will This Eat Me?

Frogs need to make this life or death decision very quickly since they could be eaten if they do not move fast enough. If they think they saw prey, but actually spotted a predator, they may get eaten. If they think it is a predator, frogs may employ one of their many self-defense mechanisms. Having excellent vision is key to helping frogs make the right decisions at the right time.

Frogs can adjust their eyes like a camera lense to help them decide to eat or run. They are very sensitive to movement and are very good at deciding which action to take depending on what is around them. Frogs can also sense things with their skin, like vibrations in water or on land which also helps them in decision making (CTNF).

5. Frog’s Pupils Can Be Horizontal or Vertical

Frog pupils are generally horizontal or vertical depending on the species and their main activities. Frogs with horizontal pupils are generally more active during the day, whereas frogs with vertical pupils are generally more active at night.

Frogs with horizontal pupils are generally more active during the day and include European Tree Frogs, American Bullfrogs, and Wood Frogs. Frogs with vertical pupils are generally more active at night like Red-Eye Tree Frogs.

There are some exceptions to frogs having primarily horizontal or vertical pupils. Vietnamese Mossy Frogs have round pupils like humans, and Oriental Fire Belly Toads have heart-shaped pupils. 

6. Frogs Can See in Color

Frogs can see in color and are particularly sensitive to tones of blue and green. Although their vision is wider than humans, it is more blurry and so colors tend to be more homogeneous and less defined compared to human vision.

Like many animals in the wild, frogs can see colors, but are more sensitive to certain colors compared to others. During the day, frogs can see some color, but certain tones are more prominent than others. They can see more than what humans can with regards to their field of vision, but their sight is more blurry. 

You can compare what frogs can see in the daylight compared to humans in this really neat tool on this Yale University site.

7. Frogs Can See in Color in The Dark

Contrary to humans, frogs can see very well at night, and they can see in color. Even if it is pitch dark outside, frogs can observe their environment in tones of blue and green.

This is incredibly useful to frogs, especially those that are active hunters at night. No matter what, frogs are very sensitive to movement and have to quickly decide if what they noticed is a predator or prey. Having the ability to observe their environment in color while in the dark is an important advantage that can help them survive being eaten.

You can compare what frogs can see in the daylight compared to humans in this really neat tool on this Yale University site.

8. Some Frogs Have Red Eyes to Scare Predators

Red-Eyed Tree Frogs have red eyes to deter predators. Primary colors generally indicate poison in the wild, and although these frogs are not poisonous, their red eyes make them look much less appealing for predators to eat. 

Having green skin that can camouflage, and covering their eyes with their nictitating membrane allows Red-Eyed Tree Frogs to become practically invisible when stuck to vegetation. If a predator gets close, these frogs can open their eyes to scare them. They may also have bright primary colors like red or blue on their legs which they may unfold to further deter predators.

A Toad Discovered With Eyes in Its Mouth

There was a toad discovered in Ontario, Canada with eyes in its mouth in the early 1990’s. This is not a normal condition and was said to be the result of a parasite infection or a macromutation that caused a gene-level adaptation.

Screencapture From Reddit
Toad With Eyes in Mouth – Reddit, Screencapture

The cause is a parasite whereas scientists believe it was a macromutation. If you ask me, Hamilton Ontario is a pretty polluted city and so this could have been an outcome of years of dumping waste into Canadian waterways.

However, very few observations of frogs or toads having their eyes in their mouth have since been made.

Sources

Thresholds and noise limitations of colour vision in dim light, Almut Kelber, Carola Yovanovich and Peter Olsson Published: 5 April 2017 https://doi.org/10.1098/rstb.2016.0065

Ewert, J.-P. The neural basis of visually guided behavior. Scientific American, 230(3), 34-42, 1974.

Ewert, J.-P. Neuroethology: an introduction to the neurophysiological fundamentals of behavior. Springer-Verlag, Berlin/Heidelberg/New York, 1980

Ewert J.-P. Motion perception shapes the visual world of amphibians. In: Prete F.R. (Ed.) Complex Worlds from Simpler Nervous Systems. Cambridge, MA, MIT Press, pp. 117–160, 2004

Are These Frogs with Eyes Inside Their Mouths Real? How else should a frog watch what it eats?, Dan Evon, 30 April 2021

Biology 7th ed. Campbell and Reece, Pearson Benjamin Cummings. P1061.