Snakes produce a fluid that is the physiological equivalent of tears, but they do not cry in the human sense of shedding tears due to emotion. Emotional crying, which involves the limbic system, is a function unique to humans and a few other mammals. The fluid a snake produces is entirely functional, serving a mechanical purpose to maintain eye health rather than expressing feeling or distress.
Snake Eye Anatomy: The Spectacle
Snakes lack movable eyelids and instead have a fascinating anatomical adaptation that covers and protects the eye. This structure is a transparent, immovable scale known as the spectacle, or sometimes the brille. The spectacle is essentially a continuation of the snake’s skin, permanently fused over the eyeball, replacing the need for blinking. This specialized scale is the primary reason why a snake cannot physically shed a tear down its cheek like a mammal can.
The spectacle creates a minute, fluid-filled space between itself and the cornea, called the sub-spectacular space. Because the spectacle is fixed and the eye surface is sealed, there is no exposed tear film to overflow and run down the face. This physical barrier eliminates the need for the typical tear ducts and drainage systems found in animals with traditional eyelids. The spectacle is shed along with the rest of the skin during ecdysis, ensuring the eye covering is regularly replaced and clean.
Function of Ocular Fluid in Snakes
Despite the lack of traditional tear ducts and lacrimal glands, the snake eye does produce a thin, tear-like secretion to fill the sub-spectacular space. This fluid is secreted primarily by the Harderian gland, which is located inside the eye’s orbit. The main purpose of this moisture is to lubricate the cornea, allowing the eyeball to move freely behind the fixed spectacle.
The fluid also functions to trap microscopic debris or foreign particles. This debris is flushed away by a specialized drainage system that routes the fluid internally. Paired nasolacrimal ducts collect the fluid from the sub-spectacular space and drain it into the mouth near the vomeronasal organ, which is used for chemoreception. This internal drainage mechanism ensures the fluid never builds up or spills out.
Understanding Apparent Crying
The visual evidence that leads people to believe a snake is crying is usually a sign that the animal is preparing to shed its skin. As the snake approaches ecdysis, lymphatic fluid is secreted between the old skin and the new skin underneath. This fluid extends beneath the spectacle, causing the old eye cap to loosen and detach from the new one.
The presence of this fluid makes the spectacle appear milky, opaque, or bluish-white, temporarily obscuring the snake’s vision. This cloudy appearance, sometimes referred to as being “in the blue,” is the phenomenon most commonly mistaken for weeping. Once the snake sheds its entire skin, the old, cloudy spectacle is removed, revealing a clear new one beneath. Visible fluid buildup can also signal a health issue, such as a blocked nasolacrimal duct, which causes the fluid to accumulate and distend the spectacle (bullous spectaculopathy).