Spitting cobras spew blinding venom toward the eyes and face of victims with surprising accuracy, and now researchers know how they do it.
Venom spitting — a defense mechanism only — is a two-part process that's part muscle and part like a baseball pitcher psyching out batters before winding up before a throw, indicates a new study published in the latest issue of Physiological and Biochemical Zoology.
"Since the venom can cover a distance of over 6.5 feet, and the snakes appear to be very accurate, it is presumed to be a good deterrent," said Bruce Young, an associate professor of biology at Washburn University and lead author of the study.
For the study, Young and colleagues Melissa Boetig and Guido Westhoff analyzed adult, captive specimens of the red spitting cobra, the black-neck spitting cobra and the black-and-white spitting cobra.
Equipped with a special visor to protect his eyes, Young had the indelicate task of taunting the snakes by moving his head in front of them. The visor was outfitted with a custom-made accelerometer system allowing a computer to track the movements of Young's head in three dimensions.
During one experiment, the researchers also anesthetized some of the snakes and implanted electromagnetic leads to monitor a muscle that controls the venom gland, as well as the movements of the snake's head and neck.
The scientists found that before a spitting cobra releases its venom, a muscle contracts, displacing tissue barriers in the snake's fangs that normally prevent the flow of venom. More muscle contractions increase pressure within the venom gland, propelling a stream of venom out the fangs.
The spitting wind-up explained, the snakes' accuracy was still a mystery.
"When we looked carefully at the data, we found that the cobras always spat shortly after I changed the direction my head was moving," Young said.
He added that when he was moving his head, the snake was also rotating its head, winding itself up before the impending hurl.
"This really boils down to geometry," Young explained. "Since I am moving linearly at a distance from the snake, the snake need only make slight angular movements to follow me. Once the cobra starts spitting, it accelerates the movements of its head, and this enables the snake to actually 'lead' its target and spray the venom to where it thinks the target's eyes are going to be."
The researchers further discovered that spitting cobras don't release their venom as a stream, mist or cloud. The liquid poison instead sprays out in distinctive geometric patterns, typically consisting of paired ovals. The scientists suspect this increases the overall area covered by the spray, heightening the snake's chances of hitting the eyes.
Aside from causing temporary or permanent blindness, the venom, if it penetrates the open eye, can enter the victim's body, sometimes leading to additional systemic problems.
Aaron Krochmal, assistant professor of biology at Washington College, also studies snakes.
Krochmal told Discovery News that the new study "is, quite simply, top notch," and that "there are some very interesting and important findings."
Young and his team are now focusing on the snakes' vision in relation to its reaction time.