Many people wonder if snakes close their eyes, often assuming they blink like humans. However, snakes possess a unique adaptation: they do not have movable eyelids. Instead, their eyes are permanently covered by a transparent, fixed scale. This means they cannot close their eyes in the conventional sense, providing constant protection without the need for blinking.
The Snake’s Unique Eyelid
Snakes have a specialized, transparent scale covering each eye, known as a “brille,” “spectacle,” or “eye cap.” This clear scale is a modified part of their skin, forming a permanent protective shield over the delicate eye. The brille is firmly attached to the surrounding scales, preventing it from moving independently or blinking.
Its transparent nature allows light to pass through, enabling the snake to see its surroundings continuously. This unique covering serves as a constant barrier, safeguarding the eye from physical damage, dust, and debris. The brille also helps to keep the eye moist, as fluid produced by tear ducts remains as a protective layer beneath it.
Life with Permanent Vision
The fixed brille significantly impacts how snakes experience their world, particularly regarding rest. Since they cannot close their eyes, snakes “sleep” by entering a state of reduced activity and awareness, often appearing to be simply resting with their eyes open. Their brain regulates their sleep cycles, allowing them to rest effectively without the physical act of eye closure.
The brille is an integral part of the snake’s skin and sheds along with the rest of its body during a process called ecdysis. Before shedding, a lymphatic fluid builds up between the old brille and the new one forming underneath, causing the old brille to become cloudy or opaque. This temporary cloudiness, often referred to as the “blue phase,” can significantly impair a snake’s vision for a few days, making them more vulnerable. Once the shedding process is complete, the old brille peels off with the old skin, revealing a new, clear brille underneath, and their vision returns to normal.
The Evolutionary Advantage
The development of the fixed transparent brille offers several advantages to snakes, particularly given their lifestyle. This protective scale provides continuous shielding against environmental hazards such as sand, twigs, and other abrasive materials. For animals that spend much of their lives slithering close to the ground, this constant protection minimizes the risk of eye injury.
The brille also allows for uninterrupted vigilance, which is crucial for both survival and hunting. Snakes can maintain constant visual awareness of their surroundings, enabling them to detect predators or potential prey without the momentary blind spots caused by blinking. This continuous visual input supports their ability to react swiftly to changes in their environment, contributing to their success as both hunters and survivors in diverse habitats.