Scientists learn secrets of spitting cobras

[uncutdiamonds]

By Jennifer Viegas
updated 1/21/2009 1:22:15 PM ET

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.

http://www.msnbc.msn.com/id/28774770/

Interesting article on this rare defense mechanism.

[John Rees]

Wow this is really interesting. I am totally amazed at what they appear to have found. I guess there are other similar marvels like the archer fish etc. I would never have guess that a defense response would be quite so involved and precise.

I just love it!

[Bushviper]

"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."

I have never heard of this before! I am assuming that after having had venom from 6 different species in my eyes I would have noticed this. I am pretty sure this does not apply to Rinkhals, Mozambique spitter, Woods spitter, Black necked spitter, Red spitter and Asian spitter. Possibly there are other species which do have this remarkable quality.

[WW]

"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."

I have never heard of this before! I am assuming that after having had venom from 6 different species in my eyes I would have noticed this. I am pretty sure this does not apply to Rinkhals, Mozambique spitter, Woods spitter, Black necked spitter, Red spitter and Asian spitter. Possibly there are other species which do have this remarkable quality.

No published evidence for it...

[Bushviper]

No published evidence for it...

Thought so, thanks for that. "Facts" like this then bring the entire research into question.

[Iggy]

Please correct me if I am wrong, I was under the impression that a spitter basically relied on the "shotgun" effect, ie a very broad area covered, which means chances are at least some would land in the eye area, which does not imply "accuracy" as such in aiming directly at the eyes?
This in no way detracts from the marvel of the spitting mechanism, just implies a different way of ensuring effectiveness...

[Bushviper]

Iggy a couple of people have come up with different theories and some even in documentary form. They have looked at the circles the snake makes when it sprays venom and placed "eyes" on their chest to prove the snake can see that well and sprays at the eyes. All of them are very narrowly focused and not one has ever answered my questions.

Two years ago a girl was helping me carry some snakes. She had a Mozambique spitter in an opaque tub with a few tiny holes drilled in the sides. After about 500 metres we got to the place and she picked the box up from the position it was in and when it was directly in line with her eyes the snake sprayed venom and caught her fully in one eye. I checked the box and there was no other time that it had sprayed venom as the sides were clear. How did this snake know exactly when to spray the venom?

[Iggy]

I agree that they can probably see the eyes, and the obvious purpose for spitting is to get it IN the eyes - but if you have a "shotgun" type of effect then you don't need to have that much control over direction etc, and if the subject is moving then you are still likely to get some where you want it...

[MV]

I have always been interested in the "accuracy" and "target aim" of spitters, and after all the experiments I have read about, and the few I have tried, I still can not come to any conclusion.
In the few experiments I did, and the ones I have read about, there are just too many variables that effects the outcome.

Interesting thing though, I had caught a Mozambique Spitter at the lodge I used to work at, and had him bagged. I was carrying the bag in my left hand, and as soon as I stepped out of the shade and my shadow passed over the bag, the snake struck at the top part of the bag and sprayed the side of my face and neck. After closer inspection, I saw both fags protruding from the material.

Question: If these snakes strike, do they inject their venom using the same method as when they spit? My guess is that they would, as it is their fangs that is adapted in order to spray their venom.

Cheers
Martin

[Bushviper]

Question: If these snakes strike, do they inject their venom using the same method as when they spit? My guess is that they would, as it is their fangs that is adapted in order to spray their venom.

Yes the venom will be injected in the same way. The opening is on the anterior face of the fang and the glands squeeze the venom down the duct till it hits the 90 degree opening and is then projected forward.

[michael]

I would tend to agree that spitters use a “shotgun effect”. Spitters also seem to focus more on movement than on the eyes, in my opinion. I noticed this with the first spitter I kept and “tested” my theory on a couple of other species. They all seem to respond in a similar manner. Try moving your hand and you will notice how the spitter will spit towards that movement and forget about your upper body. If we agree that spitting venom is an evolutionary defense mechanism focused on defending the snake from predation and from accidental damage then spraying venom upwards toward movement would be an advantage as the snake should have a good chance of getting the eyes. The chance of this happening using the “shotgun effect” would be significantly improved. Apart from extremely painful and irritated eyes I also have never heard of other systemic effects after venom has entered the eyes. It would be very interesting to get some published work on this.