Blue-eyed cottonmouths can be seen in late summer heat. It’s not a trick of light

Cottonmouths with pretty blue eyes are turning up in murky wetlands across the Southeastern United States, and it’s not an illusion.

The striking change is a very real transformation in the venomous snakes that often goes unseen by humans, due to the elusive nature of the cottonmouths (also known as water moccasins).

Timing is unpredictable, but it often happens in late summer, according to Frederick Boyce, a herpetologist with the N.C. Aquarium at Pine Knoll Shores.

“There is an old saying that ‘the snakes are blind in the dog days of summer.’ Unlike most things you hear people say about snakes, there might actually be a bit of truth to this one,” Boyce reported on Facebook.

“When snakes are getting ready to shed their skins ... they produce a creamy, bluish fluid underneath the skin that will help moisten and loosen the old skin. ... The bluish fluid is much more apparent in the eyes than anywhere else on the snake. I have little doubt that this old folk saying arose from snakes being seen when their eyes are clouded and blue in preparation for shedding.”

The process can last a week or two (depending on the species), and the snakes typically have impaired vision during that time, he says. This compels them to stay in a “secluded place” — another reason the eye change in copperheads is seldom witnessed.

Boyce shared photos of multiple blue-eyed cottonmouths with his Facebook post, taken at a coastal spot he calls Cottonmouth Acres. The 24-acre site is a large tract of restored wetland in eastern N.C. and is home to about 100 “resident” adult cottonmouths and their offspring, plus additional “transients” passing through while looking for food.

A Facebook page devoted to the site’s snakes and their daily activities has more than 7,700 followers.

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“I do seem to encounter a lot of these opaque snakes during ‘the dog days,’ but can’t say if it’s really any more likely to occur (in late summer),” Boyce says.

“Expectant mother cottonmouths, often seen basking in July and August, will go through a shed cycle before giving birth, and the baby cottonmouths, born in late August or early September, will become cloudy almost immediately, on their first or second day, shedding for the first time about a week later.”

The Carolinas are home to the Eastern cottonmouth, a species that averages 4 feet in length but can reach 6 feet, according to the N.C. Wildlife Resources Commission. Their venom is toxic to humans, but it is considered less dangerous than rattlesnake and coral snake venom, the commission says.

There’s a commune of venomous cottonmouths on NC coast, and they have a Facebook page