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Can Lizards See In The Dark?

by Lucy

Humans rely on their sight for many things – the way we perceive things, the food we choose to eat, the way we learn, the clothes we wear, and how we react to our environment. It goes without saying that, for those of us who can see, vision plays a monumental part in the way we live our lives. It’s also safe to say that vision is just as significant to animals as it is to man.

Many experts believe that reptiles do not have a very sharp sense of sight. But, recent studies and research is proving that most animals, even reptiles, have better vision than humans. Many reptiles, such as snakes, rely upon their other sensory prowess, such as their sense of smell and taste, to navigate through the world.

However, lizards rely primarily on their sense of sight. Lizards can see colors and use colors to communicate and make decisions, and some can see colors in very dim light.

So, can lizards see in the dark? Some lizards, like geckos, can see in the dark. In fact, they can see so well that not only do they perceive movement and shapes, but they can even see some color at night due to the many light-sensitive rods and cones in their eyes. Nocturnal lizards can travel and hunt in near complete darkness.

Let’s delve deeper into the subject at hand and find out more about how well lizards can see in the light and in the dark.

How Well Can Lizards See?

The most amazing aspect of the lizard is the fact that these creatures bear such a resemblance to the dinosaurs of the prehistoric age that they are labeled as the descendants of dinosaurs. But, lizards come with the ability to adapt to changing times and circumstances. Crested geckos, for example, used to be diurnal. They had more rods than cones in their eyes. 

But, as their ancestors needed to adapt to the change in times, they lost their rods and developed cones. So, now, the crested gecko sleeps through most of the day. And their pupils are vertical slits that control the amount of sunlight that enters the eye.

At nighttime, the pupils are open wide, and the crested gecko does see fairly well, even to the point of distinguishing some colors through the darkness.

Even the bearded dragon with two eyes situated at the side of its head can see with a broader range of vision than humans. Humans, with our eyes in front of our faces, can see clearly what is before our eyes and get peripheral vision to our shoulders. But, the bearded dragon can look ahead and still have the visual range to be able to see over its shoulders at the same time. 

The Reptilian Eye

The reptilian eye is such that each eye is a sphere filled with liquid (aqueous humor and vitreous humor) to keep it from collapsing. The outside wall is called the sclera. The inside of the sclera is lined with a pigmented sensory layer which is known as the retina. 

The outside of the sclera is covered by a transparent layer called the cornea, which covers a round hole known as the pupil. The iris is the pigmented muscle that determines the size of the pupil. Behind the pupil and iris is the lens through which light passes, enabling the reptile to see.

Like humans, lizards change the shape of their pupils to focus on nearby objects or things at a distance. Most lizards have round pupils, but nocturnal lizards, like the crested gecko, have vertical pupils. Not only does the vertical pupil limit the amount of sunlight that enters the eye, but the vertical pupil also helps bring objects in the distance into better focus. 

According to a study by Richard Shine and Francois Brischoux from the University of Sydney, Australia, the pupils of reptiles seemed more closely associated with hunting behavior rather than their nocturnal activity. 

They compared the pupils of 127 snake species and discovered that snakes that ambush their prey at night have vertical pupils, and diurnal snakes that actively seek out their prey have round pupils. There seems to be a similar trend in lizards.

How Does The Lizard Eye Function?

Lizards are reptiles and are closely related to snakes. The scheltopusik is a lizard that even resembles snake. In general, lizards have small heads, short necks, long bodies, and even longer tails. But, unlike snakes, lizards have moveable eyelids. 

Now, the eyelid of a lizard serves the same function as the eyelid of humans; it cleans and protects the eye. But, some lizards can’t blink, such as the gecko. Geckos have a clear membrane that protects their eyes from dirt and UV rays. These geckos use their tongues to clean up the dirt that might accumulate close to or around their eyes.

Most lizards have eyes like that of vertebrates. In short, the pupil of their eyes allows light to pass through a lens; the light centers on the retina, which stimulates the photoreceptor cells. These photoreceptor cells change the light impulse into electric impulses that travel to the brain for interpretation. 

Now, vertebrates have two different types of photoreceptor cells – rods and cones. The rods detect light when levels are low, and cones detect color. The cones contain a pigment that filters the light allowing animals to see color. In some lizards, the cones transmit ultraviolet light. 

Nature seems to gift animals sensory prowess suited to them according to their sleeping and hunting habits. Most nocturnal animals don’t see color too well at night. So, when a closer look was taken, animal experts discovered that nocturnal animals have eyes that contain many rods and fewer cones. 

But, the gecko, even nocturnal ones, can see reasonably well, as it has three sets of cones in its eyes. According to research conducted by Lina S.V Roth and Almut Kleber of the University of Lund, Sweden was able to demonstrate through their work that helmeted geckos were able to clearly make out colors of gray and blue in lighting levels that were as dim as moonlight. 

Oddly enough, animal experts were even able to discover the third eye of some lizards, like the bearded dragon, called the parietal eye. The parietal eye is located on the top of the lizard’s head, and its function is to determine light levels.

According to a study conducted by King-Wai Yau of John Hopkins Medicine in 2006, the parietal eye was able to differentiate colors, mainly blue and green. The ability to tell the difference in color possibly allows the lizard to determine the time of the day and certainly influences the basking behavior of lizards. 

Why Do Lizards Need To See Color?

As you must know, there are over 4675 lizard species around the globe, including chameleons, iguanas, geckos, and monitors. Even the 300-pound Komodo dragon falls into the lizard category.

Chameleons and anoles both show how they make use of color not just to discern the identities of other species but also to display their moods and interpret the moods of others.

Chameleons change color to show aggression, dominance, receptivity, submission, and non-receptivity to their own species. Male chameleons change color to attract females or to chase away competition. 

Similarly, anoles, too, make use of dewlap, which is a loose fold of skin hanging from the neck or throat of an animal. These dewlaps are brightly colored and work as flags of identification among anoles. Anoles even make use of color during decision-making, as a study conducted by Manuel Leal and Brain Powell of Duke University clearly showed. 

Their work published in the Journal of the Royal Society: Biology Letters indicated that during an experiment with anoles, different colored discs were used to hide treats for the anoles, and the colored disc that hid the treat was the one the anoles would repeatedly choose to receive rewards. 

Final Thoughts

Lizards are amazing creatures to look at and observe. While lizards may have a certain air of mystery, there’s no changing the fact that most lizards, particularly the crested gecko and bearded dragon, make fabulous pets.

In recent times, lizards such as geckos or chameleons have gained much popularity as domestic pets.

Not to mention, most lizards tend to do much better in captivity than in the wild. Lizards are low-maintenance pets, as they don’t eat too much, require little upkeep, and do pretty well when left on their own in a suitable enclosure.

Animal experts are intensely interested in discovering as much as possible about the lizard as they possibly can. Lizards can see well not just in the night but during the day too.

Up Next: Do Crested Geckos Like To Be Held? – Are They Affectionate?

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