Snakes, Lizards, and Tongues

His work has already shown why snakes have forked tongues. Now Kurt Schwenk, professor of ecology and evolutionary biology in the College of Liberal Arts and Sciences, is studying the biomechanics of tongue flicking. He is also working on a book about his experiences as a zookeeper at the Bronx Zoo.

<p>Kurt Schwenk. Photo supplied by CLAS</p>

Kurt Schwenk, professor of ecology and evolutionary biology, with Bob the snake. Photo by Dan Buttrey

You work with snakes on a daily basis and are often photographed holding or examining them. Did your fascination with them begin when you were a youth?

For reasons I don’t completely understand, herpetologists (people who study amphibians or reptiles) typically develop a very early obsession with the animals. They’re usually out grabbing frogs and snakes from about the time they can walk. For me it didn’t work that way. I have always loved animals, it is true, and I found reptiles of all sorts especially interesting, but it was more a casual interest than a passion. I was very fortunate in growing up in a home with lots of pristine forest around it, so I spent a LOT of time during adolescence prowling the woods and swamps. Finding turtles and snakes was always a big plus, but I didn’t think about them seriously until college.

Before then, if I thought about pursuing my interest in animals as a career at all, it was more along the lines of dinosaurs and vertebrate paleontology. But in college I became disabused of this idea quickly when it came home to me that one could never really test one’s ideas about them – it would just be too frustrating never to know anything for sure!

Fortunately, an inspirational teacher and his course on comparative vertebrate anatomy got me turned onto reptile anatomy and function, and that’s what really set me on my path. In the interest of full disclosure, I point out that my main research focus has always been lizards – snakes are an occasional thing. But in a photo it looks much cooler to be holding up a big venomous snake than some puny lizard.

Many people claim to be deathly afraid of snakes. What advice do you have for them?

I give a lot of talks and live reptile demonstrations in the community. What I have observed is that when dealing with very young children, virtually none of them are afraid – they all want to touch and handle the snakes. However, as the kids get older, more and more of them become afraid, so that by the time I am dealing with adults, many of them – sometimes even most of them – won’t come near the snakes, and a few even have to leave the room! This suggests to me that a fear of snakes is learned and not innate. I watch how parents react in front of their kids and it is very clear that they convey, however unintentionally, their own fear. I am sympathetic, however – as happy as I am to mess with snakes, even venomous ones, spiders that dart around unpredictably really creep me out!

As for advice, I think education and positive experience/reinforcement are key. The best way to get over your fear is to have someone you trust hold the snake, keeping its head away, while you touch it and prove to yourself that it’s not disgusting. One quickly learns that snakes are not slimy, that they are, in fact, warm, smooth, and muscular – they don’t feel like anything else, especially when they move in your hands. It’s really marvelous. The next step is to hold the snake yourself. They are so beautiful to look at and their movement is so remarkable – it is very powerful and controlled – that most people begin to see the snake in a more positive light. They are far less terrifying when you actually experience and demystify them. Again, you need to trust the handler so that when he or she assures you that the snake will not bite, you can be sure it won’t. I have a pet snake ‘Bob,’ who is the most gentle, sweet-tempered snake I’ve ever known. Bob has personally converted dozens of former snake-haters.

You were one of the lead researchers who discovered why snakes have forked tongues. How did you discover that?

Strangely enough, most of my research revolves around snake and lizard tongues. And yes, I get made fun of a lot. But I got interested in these quirky bits of anatomy in graduate school because they are so incredibly diverse in form – unexpectedly so, compared to other animal groups. No one understood why there was so much variation in the group, and my goal was (and is) to figure out why.

My early work concentrated on feeding because it seemed the obvious direction to go. But I also became interested, at first in a kind of peripheral way, with so-called ‘tongue-flicking’ behavior. We know that this is a chemical-sensing behavior – the animals collect odor molecules on the tongue tips and bring them back into the mouth where they are delivered to two tiny sensory organs above the palate. It’s a kind of secondary or accessory sense of smell (not taste!) that most terrestrial animals have, but sadly, not primates like us. I wondered how this chemosensory function of the tongue played off against the feeding function in evolutionary terms, so I worked on chemoreception a bit and in 1993 I was invited to an international conference on this topic. That experience really got me to thinking about the problem of how the tongue worked as part of a sensory system. I did a lot more reading and I guess I had a lot of disparate facts swimming around in my head, disorganized, as my head usually is.

One day, an EEB colleague asked me a casual question while we were standing in the departmental office – “Hey, why do snakes have forked tongues?” In that moment I had one of those epiphanies that I think most scientists and scholars live for. In a flash, all the disparate facts jelled and I knew the answer. I practically bolted to my office to write it all down! (The answer? – the two tips collect different amounts of chemical and provide directional information in a single tongue-flick, like stereo smell – it helps snakes to follow chemical and pheromone trails left by prey and mates.) In retrospect it seems incredibly obvious, and I think it probably was to some people, but no one had provided the evidence necessary to support the hypothesis, which I was able to do.

Before you earned your Ph.D., you were a zookeeper at the Bronx Zoo in New York. But there, you worked with mammals. Do you work with mammals at all now? What made you switch to reptiles?

The truth is that the only reason I worked in the mammal department at the zoo is because I couldn’t get a job in the reptile department. During college I had worked as a volunteer intern in the reptile house for a summer, but when I graduated there were no paid positions available. Although I was disappointed, it turned out to be a good thing – I got lots of hands-on experience with all kinds of cool and exotic mammals, an experience that really broadened my horizons and on which I still draw today (one of the things I now teach at UConn is mammalogy!).

It was also a pretty interesting job in a bizarre way, although the work was often difficult. But so many weird and funny things happened to me in my short time as a professional zookeeper that, after telling stories about them for so many years, my family encouraged me to put them down in a book. So I am slowly working on a series of short essays about my experiences (like the 14-foot king cobra that escaped; the giraffe that sneezed all over my face; the giant, belligerent, Malaysian tapir I accidentally released from its cage; or the day I was attacked by a giant anteater/pack of vicious peccaries/pygmy hippopotamus/guanaco/rhea (take your pick), etc. But I never left reptiles behind, and when I went back to grad school, it was always with the intention of working with them again.

Do you keep any animals of your own?

At home, we have Bob, the corn snake I mentioned before, and also Buster, the very large iguana. I should note here that Bob and Buster were both named by my son when he was very young. Until recently, we had a beautiful dog, a huge, fluffy white Great Pyrenees named Bear (I never noticed the ‘B’ theme in pet names before this moment!), but he got old and died. Animals are a pleasure to have around, of course, but I never cease to be amazed at how much biology I learn from them. If you want to learn about animals, you really have to be around them, watching them.

What is your current research focused on?

<p>Schwenk Velocity. Photo provided by Kurt Schwenk</p>

The air flow/velocity of a snake tongue flick. Image by Kurt Schwenk

Right now I’m really excited about some work I am doing with one of my graduate students, Bill Ryerson. We are interested in the biomechanics of tongue flicking in snakes. In other words, we want to know at a detailed, mechanistic level exactly how the behavior helps snakes to pull odor molecules out of the air and concentrate them on the tongue tips.

Some time ago I realized that the process must involve the diffusion of chemicals into the salivary fluids coating the surfaces of the tongue tips, and I thought that the extremely rapid, oscillatory tongue-flicking behavior of snakes might be a way to increase the speed at which this notoriously slow process occurs. In order to test this idea, we needed to look into the ‘fluid dynamics’ of the behavior, i.e., we had to visualize how the air moves around the tongue tips during an actual series of tongue-flicks. Bill figured out a way to do this using suspended cornstarch particles in the air illuminated by a sheet of laser light. While the snake is positioned to flick its tongue tips through the laser light sheet, we use a high speed (slow motion) video camera to record the air/particle movement. A computer program then calculates the rate and direction of particle movement and produces brightly-colored images that show the pattern of air flow around the tongue tips.

My brain nearly exploded when I saw the preliminary results! The snake’s tongue actually creates two pairs of counter-rotating vortices of air as it moves up and down. Each vortex is like a little donut of air moving very fast in a circle, but the donuts in a pair move in opposite directions. The tongue tips pass right along the edges of these rotating donuts of air, moving against their direction of rotation. This creates what is a called a ‘counter-current exchange’ system that should vastly increase the speed of chemical diffusion into the saliva on the tongue’s surface (most biological and engineered systems that require efficient heat or gas transfer use a counter-current mechanism). This result very strongly supports the original idea – that rapid, oscillatory tongue-flicking in snakes is an adaptation for increasing the speed (and quantity) of chemical collection on the tongue tips.

While I expected some kind of air mixing, the extremely organized pattern of airflow came as a real shock to me. It was another one of those incredible intellectual high points in my career. It’s a very important result and it has already generated a lot of interest at meetings. Now we just need to get it written up and published!