How Snakes See Two Ways

Jan. 9, 2002 -- As a kid growing up in the rolling hills of central Georgia, Michael Grace loved to walk around with a pocket full of snakes.

"Most people were terrified of them," including his mom, which made life around the Grace home a little awkward at times, he says all these years later.

But to a kid in Georgia, that just made snakes all the more interesting.

As the years passed he turned his hobby into a profession. Now, he spends his time probing the world of snakes in his laboratory at the Florida Institute of Technology in Melbourne.

The secrets he is learning from the fascinating reptiles that live in his lab could someday lead to major advancements in everything from heat seeking missiles for the military to tiny devices that might help physicians locate tumors in the human body.

That's because pit vipers, like rattlesnakes, and the group of snakes including pythons or boas can literally see the world in two different ways. They can use their eyes to create a visual image of the world around them, just like humans do, or they can use their extraordinarily sensitive infrared sensors to create a similar image based upon heat emitted by objects in their environment.

They can switch back and forth between those two systems, or use both simultaneously, giving them a leg up, so to speak, when it comes to targeting a warm object.

Snake-Eyed Missiles

What has intrigued Grace for years now is how snakes are able to do so much with so little. A rattlesnake, for instance, has one small pit on each side of its head, filled with thousands of receptor cells, which are actually microscopic-sized infrared sensors. Yet despite their tiny size, the sensors are at least 10 times more sensitive than the best artificial infrared sensors that have ever been built, says Grace, a biology professor at Florida Tech.

Unlike artificial sensors, they don't require an elaborate cooling system, and they can repair themselves if damaged.

All of which set Grace to thinking.

"If you can build a sensor that's based upon the cell biology and biochemistry" of snakes, he says, "you could make some extraordinary advancements in artificial sensor technology."

So a couple of years ago he landed a $365,800 three-year grant from the U.S. Air Force Office of Scientific Research to see just what snakes might be able to tell us about infrared vision. That could come in handy for such things as a heat-seeking missile that could fly up the exhaust valve of an enemy aircraft without revealing its presence.

Grace's personal quest, however, was more in the line of scientific curiosity. He just wanted to learn how these animals are able to convert infrared radiation — or heat — into a signal that can be processed by the central nervous system, giving the snake a second source of vision.

He wanted to know which system is most important to the snake, eyes or infrared sensors? Can snakes get by with just one system if the other fails? Can they switch back and forth between the two systems?

Snake Patch Science

To answer questions like those, Grace and several colleagues had to figure out how to shut down some of the snakes' abilities, like their eyesight, for example, to see which components did what.

But no lover of snakes is likely to poke their eyes out. So the researchers came up with a benign approach: electrical tape.

"For the eyes, we simply put a little patch over the eye," he says. When the snake later sheds its skin, as all good snakes do, it sheds the patch as well.

"It's very safe for the animal," he says.

A similar procedure worked for the infrared receptors.

That allowed the researchers to zero in on the various components of the snakes' systems, and the research has turned up some surprising findings. The infrared sensors can detect wavelengths of 10 micrometers, and "that's extremely low-energy radiation," Grace says. That means that a snake can "see" a warm-blooded animal even with its eyes closed.

The infrared sensors are actually receptor cells in the pit organ, and the research indicates that they come in different varieties, possibly to "look" at different wavelengths in the infrared. That would give the snake a sort of "color vision," according to Atsuko Matsushita, a visiting scientist at Florida Tech who is working on the project.

With the help of the electrical tape, the researchers found that their subjects were able to get along quite nicely, even if temporarily impaired. If they blocked out the eyes, the snakes functioned with just their infrared sensors. If the researchers knocked out those sensors, the snakes used their eyes.

Thus the snakes were able to switch back and forth between the two systems.

Detecting Tumors

All of this suggests that the reward for borrowing technology from snakes may be very high indeed.

Grace, who studied at two medical schools before returning to his passion for snakes, believes that if we could somehow replicate the extremely sensitive infrared sensors of the pit viper, it might be possible to detect very small temperature changes in parts of the human body.

A tumor, for example, requires an increased flow of blood to grow, possibly resulting in a slightly elevated temperature around the tumor.

Any change would be so small, Grace says, that "no detectors that we have available now would be able to detect it."

But a snake might know it's there.

Someday, because of what snakes might be able to teach us, a physician might also find that tumor before it spreads.

Lee Dye’s column appears weekly on A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.