Curious question for the Year of the Snake! What does the world look like from the perspective of a snake?

Review expert: Wang Lei, National Park and Nature Reserve Researcher, PhD in Ecology

Editor's Note

The Year of the Snake is here. How much do you know about snakes? Beijing Science Center has carefully planned a series of popular science columns titled "Curious Questions in the Year of the Snake" to explore the wonderful world of snakes from a scientific perspective and start a wonderful journey of exploring the science of snakes in the new year.

Snakes are often seen as mysterious and frightening creatures. Many people are afraid of snakes, and this fear may come from a natural alertness to the unknown and potential dangers. However, when we take a closer look at the anatomy of snakes, we find that they are not as dangerous as we think.

0 1Snakes generally have poor eyesight

Snakes have eyes on both sides of their heads, which makes it difficult to form a three-dimensional visual perception because the overlapping range of the two eyes is very small. They can only see things very close to them, and most snakes cannot even see objects one meter away, especially stationary objects.

This vision defect explains why, in some cases, if a person can remain still as a snake crawls onto them, they are less likely to be attacked.

In addition, the structure of snakes' eyes also limits their visual clarity. The sclera of snakes is opaque and can protect the eyeball; although the cornea of ​​snakes is transparent, the pupil in the center cannot adjust its size freely to control the light entering like the human eye.

Snakes' vision is further limited in bright daylight, but is relatively sharper at night or in dim conditions. However, not all snakes have equally poor vision, and some cobras have relatively good vision.

0 2Snake Eyes is similar to an infrared camera

Snakes have a unique sensory ability to make up for their lack of vision: thermal sensing. Near the nostrils of snakes, there is a pair of heat-sensitive sensors called "pits". These sensors can sense any object with heat around them, just like an infrared detector.

For snakes, the world around them is presented as a source of heat. This ability allows snakes to easily sense the body temperature of animals at night or in dim environments, helping them hunt.

Pictured is the "Animal Vision" exhibit at the Beijing Science Center

0 3Are snakes’ pupils vertical?

The shape of snakes' pupils varies depending on their habitat. Diurnal snakes usually have round pupils, while nocturnal or crepuscular snakes have vertical oval pupils (vertical pupils). This pupil shape allows for better control of the amount of light reaching the retina to adapt to different lighting conditions.

0 4What is the difference between horizontal pupils and vertical pupils?

Vertical pupils can assist the eyes' stereoscopic vision, making it easier for animals to measure the vertical distance of objects; at the same time, animals can measure the horizontal distance of objects from themselves through the degree of defocus blur.

Therefore, nocturnal and diurnal ambush predators usually have vertical pupils, such as cats, snakes, etc.

Most animals with horizontal pupils have eyes on both sides of their heads. Wide monocular vision can help them have clear horizontal panoramic vision to detect predators from different directions, and also allow them to see the ground in front of them clearly even with their eyes on both sides, so they can escape quickly when being chased. Interestingly, no matter where the head of animals with horizontal pupils is, their pupils can remain parallel to the ground.

Therefore, herbivores that are prey usually have horizontal pupils: such as zebras, sheep, etc.

In the eyes of snakes, the world is a blurry and heat-filled scene. They rely on heat sensing to search for traces of prey, while vision is more used to distinguish environmental colors, shapes, and dynamic changes. Although snakes have limited vision, they have developed a visual system that adapts to their ecological niche during the long process of evolution, allowing them to survive and reproduce in a complex and changing environment.