Our fear of and fascination with snakes

By Jeff Mitton

A smooth green snake, Opheodrys vernalis, moved quietly through the grass at Chautauqua Park, away from a cluster of people assembled for a picnic.

But someone with sharp eyes noticed the green snake in the green grass, and shortly thereafter I had it wrapped around my fingers.

Adults of this species are typically in the range of 14 to 20 inches long, and this one was close to the upper limit. It had a tan head, green back and sides and a light yellow belly. The scales on the sides and back were especially smooth, giving the snake a silky feeling. It did not thrash or nip, so I was enjoying showing it to children until it musked me.

Snakes have a pair of musk glands or anal scent glands used in defense against predators, attraction of a mate and marking their territories. I find the use of the musk scent quite effective, for I transitioned from fascination with the beautiful and colorful snake to revulsion in seconds. I released the snake and went to wash my hands. The snake went slowly on its way.

Smooth green snakes are native to Colorado, and their geographic range stretches from the southern Rocky Mountains to Nova Scotia. Their diet consists of small insects, spiders, caterpillars, moths, snails and slugs.

When I was showing the snake to children, I noted their reactions as well as the reactions of adults who clustered around. Most people were intrigued, but a few adults were apprehensive.

Ophidiophobia is an abnormal fear of snakes. For the afflicted, this is no laughing matter; they don't want to encounter a snake, see a snake on television or in the movies, or even look at a picture of a snake. Many people fall short of ophidiophobia but are still not comfortable in the presence of snakes.

Do humans have an innate fear of snakes? The answer is not clear.

Some studies suggest that children who have never had any experience with snakes fear them at their first encounter. Other studies suggest that these fears have been planted by what the children have been told or what they overheard. However, studies of human vision have unambiguously established that both naive children and experienced adults can pick out the image of a snake in a photo faster than any other image.

The same is also true of monkeys. So it seems that humans and monkeys have a heightened vigilance and interest in snakes. Personal experience leads some to enjoy snakes, others to fear them.

Snakes don't blink, a trait that makes some people uneasy. A snake's eye does not have an eyelid, but is covered by a clear scale that protects it and keeps it from losing moisture. I have seen garter snakes whose eye scales were scratched or abraded by bumping into objects or digging into the litter and soil. But as a snake grows, it periodically sheds its skin, peeling off the scratched and pitted eye scale and exposing a fresh, clear scale.

Pupil shape varies among species of snakes -- some have round pupils, others have vertical slits. Snakes that actively forage during the day usually have round pupils, whereas those that are ambush hunters at dusk and during the night usually have vertical slits. The vertical slits provide good depth of field while admitting much light and may also help the snake blend in with its background.

Although snakes do not have limbs, they have no problem getting around, and some species have adopted the habit of climbing into trees to hunt. Five modes of locomotion are recognized in snakes, but most snakes cover ground with lateral undulation. This is a graceful, nearly silent mode in which the head and neck pick a specific path and the rest of the body follows, like the cars of a train following an engine. The snake is driven forward by muscular waves traveling posteriorly, pushing against fixed irregularities in the environment, such as ridges on a stone surface.

Jeff Mitton (mitton@colorado.edu) is a professor in the Department of Ecology and Evolutionary Biology at the University of Colorado. This column originally appeared in the Boulder Camera.

August 2012