Cobras Spit Venom at Eyes With Nearly Perfect Aim
for National Geographic News
|February 10, 2005|
If you're smart, you'll never come within six feet (two meters) of a spitting cobra. If you're unlucky and by some horrible chance you do, a word of advice: Close your eyes.
Katja Tzschätzsch, a research student at the University of Bonn in Germany, has demonstrated that the red Mozambique spitting cobra and the black-necked spitting cobra deliberately aim for the eyes of whomever or whatever they feel threatened by.
The lab results don't surprise snake experts.
"To my knowledge there hasn't been a lot of work done on whether they actually aim for the eyes. It's mostly been anecdotal evidence," said Bill Altimari, a herpetologist at the Arizona-Sonora Desert Museum. "But I'd be surprised if anyone in the field thinks otherwise. My experience has been that the red spitter and the black-neck went right for your eyes. Our keepers at the Philadelphia Zoo [where I used to work] always wore face masks."
Sam Lee, assistant supervisor in the Bronx Zoo's department of herpetology, concurs, again based on personal experience.
"These animals always aim for keepers' goggles," he said.
"Anyone at the zoo working with this type of snake wears a face mask because that's usually where they aim," added Dino Ferri, assistant curator for reptiles and amphibians at the Audubon Zoo in New Orleans.
If everyone knows spitting cobras aim for the eyes, why ask the question?
"It was necessary to actually show this in order to ask the next question: How do cobras identify the eyes in different animals and humans?" said Guido Westhoff, the professor at the University of Bonn who supervised Tzschätzsch's work.
Katja Tzschätzsch used four red Mozambique and six black-necked spitting cobras. In her experiments she either stood face-to-face with themprotected by a plastic visoror she used photos.
She recorded the spitting process using a high-speed video camera. "The snakes really do spit only at moving faces," was her first finding. "Movements involving the hand elicited no response from any of the snakes."
Only two cobras reacted to photos of faces.
The evaluation of the traces of venom on the photos and the visor revealed how accurate the both species' aim is: The black-necked spitting cobras hit at least one eye eight out of ten times. The Mozambique cobras hit their target every time.
What happens if a cobra's venom lands in your eye? The cocktail of toxins consists of nerve poisons and other components harmful to tissue. The sensitive cornea reacts with severe stinging pain. In the worst case these burns can lead to blindness.
The lesson is clear: If ever you're confronted by a spitting cobra (common in Africa and Asia) stand back at least 10 feet (3 meters) and protect your eyes.
Spitting vs. Biting
Not all cobras can spit. Those that can have a specially modified fang with a small hole in it.
"When the snake contracts its venom gland, it squeezes a small amount out at high pressure. The venom hits the floor of the fang hole, bounces upward and out," Altimari said.
Why spit instead of bite? Spitting is strictly for defense, the experts say.
"The snake will spit at something bigger than it, and feast on something smaller," said Ferri, who is the chairperson for the American Zoo and Aquarium Association's group that advises on the scientific classification of snakes.
Non-venomous snakes like boas and pythons grab their prey and squeeze them to death. Cobras, however, use venom to kill. But cobras are not particularly muscular, and their fangs are relatively small. To kill their prey, they need to bite and hang on.
"It's not the best venom-delivery system," Altimari said. "And there's a big risk to the snake in closing in on prey. Even a rat, if the cobra doesn't disable it immediately, could turn around, bite, and kill the snake. What good is it going to do the snake if the rat dies later?"
Because of this vulnerability, cobras have developed an elaborate system of bluffing to intimidate anything they see as a threat.
To ward off trouble, cobras can rear up, and they have hoods that expand out like a half umbrella to make themselves appear bigger and scarier than they actually are. And some species can spit.
How far can they spit their venom?
Depending on the size of the snake, experts say the venomwhich is ejected with a velocity equivalent to that of a water pistolcan travel 4 to 8 feet (1.2 to 2.4 meters).
"It's fast enough that a human couldn't evade it," Altimari said.
For the cobras that can spit, it's apparently a deeply instinctive responseWesthoff was once spat at by a baby as it came out of its shell.
"I was just inspecting the eggs at hatching time," he said. "Only slight movements of my head induced the baby cobras that already emerged from the egg to look at me. One cobra that just poked the head out of the egg even spit at me."
And of course the snakes are aiming for the eyes, Altimari said.
"Really, spitting is a highly evolved trait, and if they're not aiming for the eyes, what's the point?" he said. "Venom landing on the skin isn't going to deter a threat. If the venom gets in your eye, it burns, it's excruciating, and it's immediate, and you're going to flee."
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