Belly Up: Why Do Some Snakes Have Elaborate Belly Patterns?

Snakes aren’t in the habit of standing upright. That thought prompted Dave Patrington to ask Saturday’s Weird Animal Question of the Week via Facebook: "Why do so many snakes have pattern and color on their bellies?" If you’re a ground-hugging reptile, isn’t that a waste of ornamentation?

A belly full of variations

The eye-catching checkerboard belly of the corn snake is a good example of this body décor-—it resembles an ear of maize, which is likely what inspired the snake’s name.  

But, “patterns are not very common on snake bellies," says Kate Jackson of Whitman College in Washington State. Instead, the reptiles typically display solid colors that are paler or brighter than their topsides.

This contrast is called countershading, a type of camouflage that "occurs across the majority of animal groups," says Whit Gibbons, author and herpetologist at the University of Georgia’s Savannah River Ecology Laboratory.

One example is the smooth green snake. Sunlight makes the dark green on its back appear lighter, so that it blends with the pale green on the lower part of its body. The result is a uniform color that is harder to see, especially against green grass. (Read more about animal camouflage, including countershading.)

But other colors are meant to be seen. “Red, orange and yellow are called ‘warning colors’,” Jackson says, because they are often associated with venomous species. And sometimes, the contrast of colors—such as the non-venomous  ringneck snakes, which are black on top and pale red below—serve as “flash coloration” that can briefly confuse a predator.

"When the snake is noticed by a predator and disturbed, say picked up or turned over, the startle value of the pale underside or the warning colors (yellow/orange) might buy the snake a moment to escape,” says Gibbons.

The different color schemes are also apparent in aquatic snakes. Banded watersnakes have elaborate belly patterns and spend a lot of time swimming. Their patterns "might be very effective against a predator like a snapping turtle or big fish looking up from below," Gibbons says.

By contrast, the plain-bellied watersnake, true to its name, doesn’t have an elaborate pattern. Since it spends a lot of time on land where its belly doesn't show, it benefits more from countershading than from flash coloration.

Racing stripes

Lee Fitzgerald, a herpetologist at Texas A&M University, says that the dizzying color variations of snakes can also enable mimicry.

The eastern coral snake, for example, is a venomous snake with colorful bands that signal trouble to would-be predators. The scarlet king snake is harmless, but uses its coloration to masquerade as the lethal coral snake. The two look so closely alike that a rhyme had to be invented to help us remember which is which. (Find out why the primate brain reacts so quickly to snakes.)

I asked Gibbons about the bright stripes of the San Francisco garter snake, partly because it’s so pretty and partly because, who knew San Francisco had its own garter snake?

Stripes create an "optical illusion," Gibbons says. The eye can’t stay focused on a rapidly moving animal with this pattern, but is "suddenly seeing the end of the snake disappear in the grass."

"Plus," he says, "Californians would expect nothing less than that their snakes sport the most elegant fashions."

Weird Animal Question of the Week answers your questions every Saturday. If you have a question about the weird and wild animal world, tweet me, leave me a note or photo in the comments below, or find me on Facebook.