Learn Why and How Animals’ Eyes Glow at Night

If you’ve ever walked around at night, or have a furry friend as a pet, you’ve seen eyes glowing in the dark back at you. If you don’t expect it, it is a terrifying thing, to see eyes shining back at you. However, it’s quite normal to have animals’ eyes glow at night.

To learn more about why this happens, which animals have glowing eyes, and how it works, continue reading below.

Do Animals Have Glowing Eyes?

Even though it looks like animals have glowing eyes at night, that’s not the case. They are actually reflecting light.

If they glowed, they would be lit up all the time. However, animals’ eyes only get the glow when a light source is shined at them, such as headlights, lights from a fire, or a flashlight.

What Causes Their Eyes to Glow at Night?

The reason that animals have eyes that appear to glow at night is for a few reasons. First, the animal must have large pupils. Large pupils are common in any animal that needs to see at night, as it lets more light in. Second, animals need to have a lot of rods in their eyes. The rods are what absorb light, so the more rods, the better an animal can see at night.

Third, many animals that have eyes that reflect in the dark have something known as tapetum lucidum. In simple terms, this is a thin layer of tissue that sits behind the retina and causes a reflection. It acts like a mirror, reflecting the light that entered the eye back out and past the retinas again. This layer allows animals to use the light in their environment twice; once when the light is entering the eye, and once when it is reflecting.

Every animal has slightly different glowing eyes. Some of them glow brightly, while others are fairly dim. Studies have shown animals that have the brightest glow at night when they have more rods and fewer cones in their retinas.

For those that don’t know much about eyes, this means that they can see very well at night, but are mostly colorblind.

Eye Colors

If you’ve seen a lot of animals at night, you may have noticed that animals have different colors that reflect. Big cats have more yellow eyes, while deer have green, and alligators are bright red. Unfortunately, a reason why certain animals have different colors has not yet been documented.

There are some theories, however. Some studies have shown that the pigment within the retina contributes to the colors. So too does age, it is thought.

Do Only Animals That See at Night Have Glowing Eyes?

More animals have glowing eyes than just those that see at night. However, it does seem to be limited to animals that live in the darkness. Animals that spend a lot of time in caves, or in the depths of the ocean where there isn’t a lot of light, will also have glowing eyes.

What Animals Have Glowing Eyes?

Most animals who have glowing eyes at night are that way because they are night hunters. They need more light to see at night.

Some mammals that have glowing eyes include ferrets, horses, and cows. Many nighttime predators also have glowing eyes, like bobcats and coyotes.

While we most recognize mammals having glowing eyes, there are plenty of other animals that have them as well. Some spiders, reptiles, and frogs have reflecting eyes. Alligators and crocodiles are animals well known in the South for having glowing red eyes. The wolf spider is also a unique species that has eyes that reflect at night. Bullfrogs are also easy to find when you’re hunting due to their reflective eyes in lakes and ponds at night.

Interestingly a few birds that are more active at night have glowing eyes. However, they are a little different from everyone else, as they are missing the tapetum layer. Scientists aren’t yet sure how or why their eyes glow, only that they do. One bird that has eyes that reflect the light is the nightjar.

Domesticated Animals

Dogs and cats usually have glowing eyes. However, since a lot of them are losing the need to be able to see at night, they are also losing their glowing eyes.

Dogs, especially, are showing signs of this. Dogs with blue eyes or lighter coats tend to lose the genetic trait that allows them to see at night. Pets with darker eyes will still show signs of glowing eyes, though.

The photo featured at the top of this post is © Alexey Stiop/Shutterstock.com