While walking along the path on the Dino Trail the other day, a small brown snake entered the path in front of me from the banana trees and palms that line the paved walkway. The pattern on the back of the approximately 10″ – 11″ snake immediately identified it as a copperhead.
According to the literature, copperheads are born live in late summer or early fall. They’re 8” – 9” at birth. This snake was born last year.
There was something strange about this snake. Typically, the yellow tipped tail is more obvious on young copperheads. I hadn’t noticed the tail color until I gave the snake a second look. This one’s yellow tail was fading and I passed off the “strangeness” of the snake as being related to the tail color.
The snake didn’t assume a defensive posture or freeze, raise its head off the ground and watch as copperheads typically do when approached. It simply kept crawling purposefully across the path.
Later, when I got back to my office and viewed the dozen or so photos I took of the pit viper, it became obvious the snake was missing its right eye. There was no sign of injury but a neat depression where the eye should have been, with scales over the site. My experiences with snakes suggest old wounds show on their bodies, they leave a scar on the scales. This snake was probably born without a right eye.
Pit vipers hunt the small prey they consume with the help of heat sensitive sensors (pits) on each side of their heads. The pits are located between the nostrils and the eye. They also use their tongues to sense or smell the air around them. And, they certainly feel the vibrations of any large animal moving towards themselves (like a naturalist on a paved path through the Dinosaur Trail).
So why didn’t this snake freeze, threaten, or react in any way to my standing next to it taking photos? Did it simply not see me (I was on its right side). Do copperheads perceive threats via their eyes and not the other sensors at their disposal (heat, chemical “smell,” or vibration)? Or did this snake merely not care it was being watched?
Can this snake survive with only one eye? Copperheads have evolved with eyes, so they must be useful to the animal. It would seem though, that their vision is not particularly acute spending most of their time on the ground (they do climb into shrubs). How far do they need to see? A few meters, if that, is probably all that’s necessary for a ground dwelling snake. Does the snake use it’s eyes in conjunction with its heat sensing pits, or do the two senses act independently? Do they see an image similar to what we would see when looking through the lens of an infrared camera or viewer screen?
Various snake families posses differing abilities to see. Some cobra species must surely have acute vision, they can accurately spit venom at the eyes of a potential threat (an approaching human, tiger, etc.). Some arboreal snakes have sharp vision while burrowing snakes have poorer vision. The pit vipers such as copperheads apparently rely more on their heat sensing ability that “normal” vision. And, this heat sensing ability is meant to help them locate prey, not necessarily to avoid predators.
The snake kept on course and crawled off into the leaf liter on the other side of the path. Fifteen seconds later it was gone.
I’ll keep a lookout for this snake in the future.