Harry W. Greene is professor of herpetology and director of graduate studies at Cornell University, Ithaca, New York. He qualified as a biologist at the University of Texas and the University of Tennessee. He has studied reptiles around the world from Europe, Africa and Asia to Arizona’s Sonora desert. His research focuses on behaviour and ecology, mimicry, conservation and evolutionary biology. His books include Snakes: The evolution of mystery in nature (University of California Press 1997)
How did you get involved with reptiles?
When I was about 7, I saw a horned lizard crossing a road in east Texas. It was love at first sight. I was fascinated. Soon after that my parents gave me my first book on reptiles. It has been reptiles for me ever since.
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Why did you decide to concentrate on snakes?
As an undergraduate I was an ambulance driver, then a medic in the army, so I had a lot of experience of violence and death in my youth. I developed a fascination with venomous snakes at the same time. It stems from a general interest in mortality, death, evil and so forth. Venomous snakes give us a point of reference about killing that doesn’t involve evil. They make a living killing other things and they can potentially kill us. But, if you reflect on it, you realise this has nothing to do with evil. If we get bitten by venomous snakes, it is because we threaten them or do something that makes them feel afraid, not because they have any kind of intention to do us ill.
My fascination with snakes deepened as an adult. I was looking at coral snake behaviour for my master’s degree. These are venomous, brightly coloured snakes that specialise in eating other snakes and that are mimicked by other, harmless snakes. For my PhD I was interested in a more conceptual problem: is it possible to compare behaviour across species and make inferences about what their ancestral behaviour was like? All this got me more and more into snakes.
Isn’t your fieldwork rather dangerous?
The way I learned to catch snakes as a young person was dangerous. It was fairly common to meet people who had missing fingers. There was even a joke about the herpetologist’s handshake: you’d notice a digit was missing or they had a mass of scar tissue on their palm. Notice that I have all my digits.
I have never been bitten. I don’t want to be and I would be embarrassed to be. The fashionable thing for performers and entertainers to do is to pick up snakes up and dangle them around and say how dangerous they are, but I consider that really inappropriate. I realise it sells television programmes. But I wish they would find ways to do it that did not stress the snake. When you see someone take a snake by the tail, then hold it up and wave their hand in front of it to get it to strike, what you are seeing is the equivalent of me slamming you up against the wall, saying something threatening and then taking a picture of your face and saying, isn’t she an unpleasant person.
I have been afraid of snakes only twice in the field. Both times were in Costa Rica. I was closer than I wanted to be to big dangerous vipers. Once I accidentally bumped into a bushmaster, a large and venomous pit viper. I only saw it when it moved away from my right foot after I’d just bumped it. Another time I got too close to a large fer de lance in mud – perhaps the most dangerous snake in Central America.
But I have been on a plane that caught fire, I have been in a very bad car accident, and I have had loaded guns pointed at me. I have been in far more danger from humans than I have been from animals.
Is your work ever dangerous to the snakes?
Because we want to watch individual snakes year after year, we are at pains not to traumatise them. So, for example, in our ongoing field study of rattlesnakes in Arizona we never manually restrain them. We capture them gently by lifting them on a stick into a container, then take them back to a lab and anaesthetise them. While they are anaesthetised, a radio transmitter is placed in their body cavity. Then we put them back in exactly the same spot where we caught them, our rationale being that snakes are less stressed at being in familiar surroundings than they would be in a cage. The typical response from the snake is to sit quietly for three to five days, as if it were recovering from surgery, which of course it is, and then to resume normal behaviour.
The radios last about two years. Over that time the snakes grow, reproduce and eat normally, and they show absolutely no response to our presence. They are not threatened by us. They never change their home range or their areas of activity after we interfere with them. I am convinced this is because we don’t traumatise them. We do steal about five days from them every two years. I justify that easily by what we have found out about them, things that have helped people see snakes as real animals with lives instead of evil objects.
What kind of things have you found out?
Snakes will use the same places in their home range year after year for particular purposes: for example, always going 300 metres that way under that rock to shed their skin, then always going down into this creek bottom to look for a female, and five months later crawling almost the exact same path several hundred metres up onto the same canyon ramp and going into the same little hole to hibernate. There is a lot of evidence that as snakes grow up they learn a chunk of the landscape and use that knowledge in ways appropriate to their lifestyle.
Another thing is parental care. People did not used to think of lizards and snakes as having any system of parental care. It turns out that almost all pit vipers, the group that includes rattlesnakes, remain with their babies for about 10 days after they are born. This probably helps protect them against predators.
A third finding I will illustrate with an anecdote. We knew that when rattlesnakes and other vipers hunt they use their tongues to sample scent molecules in the air. A few years ago I watched a large, black-tailed rattlesnake crawl into a ravine, approach the runway of a chipmunk and spend 13 minutes tongue-flicking the area. Then it backed into the stereotype ambush posture just off the edge of the runway in readiness for the chipmunk. There was a dead fern frond about 20 centimetres in front of the nose of the snake, right in its prospective strike path. After two minutes, it reached its head and neck out in the posture I’d previously seen used only in combat with other males, and bent the fern out of the way. It then went back to its ambush position.
Now, it’s possible to explain that behaviour as a simple stimulus response. But it’s also possible the snake did something a bit more complex, adopting a behaviour it normally uses in combat to modify the immediate environment in preparation for its strike. That is the kind of sophisticated behaviour we usually associate with some mammals and birds, not with lowly reptiles.
How do snakes use mimicry?
Mimics make a living by convincing predators that they are something they are not, that the cost of killing them is high. Let me give you an example.
When I lived in Berkeley, I owned a 40-kilogram, loyal, smart carnivore – my dog Layla. One day I was jogging with her in a park when somebody’s Doberman charged at us. My dog jumped in front of me and the Doberman grabbed her by the rump. I kicked it in the head and it ran off squealing. I was so terrified my knees were about to drop from underneath me. My dog was just excited: let’s go find another Doberman.
A week later we encountered a small gopher snake, a harmless creature about 40 centimetres long. Its teeth are so small they couldn’t even scratch the nose of my dog. But gopher snakes have a defensive display. They pull back into a striking coil, spread out the back of their head, vibrate their tail, hiss loudly and strike forward. When Layla ran up to this gopher snake it snapped into this defensive posture, struck at her and hissed. Layla ran off yelping.
I call this Layla’s paradox: why does that defensive behaviour work on a large, smart mammalian carnivore? It is a total bluff. Rationally the dog should have snapped the gopher snake in half and eaten it. The answer is that once in a while it is not a baby gopher snake, it is a baby rattlesnake. The consequence of making that mistake is so severe that predators by and large cannot afford it.
Why are you so fascinated with the predator-prey relationship?
It is an exquisitely important interaction because there is always the possibility that one of the two is going to die. It is like the dance of life, with death being a complement to life. In the west – maybe it’s just in the US – people fail to come to grips with the fact that we are mortal; that a normal part of our existence is that it ends.
Can humans and snakes live safely together?
There is a special problem co-existing with something that can kill you. If we could learn to live with rattlesnakes, we might find learning to live with lions a little easier. One answer to the question, why should we have to live with snakes, is because snakes eat rats. If we don’t have snakes, we will undoubtedly have more rats. But a deeper reason is that they are part of the diversity of nature. They are part of the natural tapestry, the natural, artistic beauty of our planet.
What is most fun about working with them?
The best thing about being a scientist is when you realise that you’ve just seen something that no one has seen before, or when you see something that just surprises you. I enjoy having my preconceptions destroyed.
Until about five years ago I thought I had a good understanding of mimicry. Then National Geographic sent me a photograph of a flatworm from Borneo that looks exactly like the coral snake. I pulled this picture out of the envelope and I had an instant of cognitive dissonance. I knew it was a flatworm, yet it couldn’t be. That led to new, interesting avenues of thought and research about mimicry. It turns out that these flatworms are noxious and extremely toxic to chickens, horses and cats. That raises the possibility that they are part of the mimicry system: they could be models or mimics or both.
What will you be studying next?
In the next few years I hope to concentrate more and more on watching animals in the field. I’m very much a descriptive biologist. I’m not an experimentalist. I made that observation about the snake bending the fern out the way, then sat on it for about three or four years thinking, this just blows my mind. What am I going to do with it?
Then last May I spoke about it to Alex Kacelnik from Oxford, who works on New Caledonian crows that make tools. So now I’m going to begin exploring it further.