The temporary loss of sight in snakes is a natural, cyclical biological process necessary for growth and health. This phenomenon occurs during the preparation for shedding their outer layer of skin. The process causes their eyes to become cloudy and opaque, significantly impairing their vision.
Separating Folklore from Fact
The idea that snakes go blind specifically during the “Dog Days” of summer is folklore connecting animal behavior to astronomy. The “Dog Days” traditionally span mid-July to mid-August, coinciding with the heliacal rising of the star Sirius, part of the constellation Canis Major. This period is historically the hottest and most humid time of year in many regions.
The myth persists because the increased heat and humidity of summer accelerate the snake’s metabolism. As cold-blooded creatures, snakes grow faster when temperatures are higher, requiring them to shed their skin more frequently during the summer months. Therefore, the period of temporary blindness preceding shedding is simply more common during the “Dog Days.”
The Biological Mechanism Behind Temporary Blindness
The scientific process of shedding the outer skin layer is known as ecdysis. This regular function is necessary for snakes to accommodate growth and remove external parasites. Unlike mammals, a snake’s skin does not expand as the body grows, necessitating the periodic replacement of the epidermis, which directly leads to temporary vision impairment.
A snake’s eye is permanently covered by the spectacle, a clear, protective scale that functions as a modified, fused eyelid. When the snake prepares to shed, a new layer of skin and a new spectacle form beneath the existing outer layer. To facilitate separation, the snake secretes a lubricating, lymphatic fluid into the space between the layers.
This fluid buildup causes the old spectacle cap to lift and become cloudy, resulting in a milky, bluish, or opaque appearance. This visual change is known as the “blue phase” and directly interferes with light passing to the retina, hindering the snake’s eyesight. This opaque phase typically lasts for a few days until the fluid is reabsorbed and the eyes clear up just before the snake sheds the old skin in one piece.
Navigating the World Without Clear Vision
The temporary visual impairment during the “blue phase” triggers immediate changes in the snake’s behavior. Since their vision is severely compromised, snakes become vulnerable to predators and are less effective at hunting. Consequently, they seek secluded, dark hiding places where they remain inactive until shedding is complete.
During this vulnerable period, the snake relies heavily on its other developed senses to navigate and detect threats. Chemoreception, the sense of smell and taste, becomes the primary means of gathering environmental information. The snake uses its forked tongue to collect chemical particles from the air and ground, delivering them to the Jacobson’s organ for analysis.
The ability to sense vibrations through the ground is also heightened, allowing them to perceive approaching threats. Because they are stressed by temporary blindness, snakes in the blue phase are often more irritable and prone to defensive posturing or striking if disturbed. They typically refuse food during this time, conserving energy for the physical effort of shedding.