The work of Thomas Eisner highlights the central role of chemistry in the living world. Dr. Eisner is a pioneer of chemical ecology, the study of the chemical language of nature. Insects are his "beasts of choice," and his research on their chemical interactions with each other and with plants has yielded insights into animal behavior, ecology, and evolution. Among his many distinctions, Dr. Eisner is a member of the National Academy of Sciences and a recipient of the National Medal of Science and the Tyler Prize for Environmental Achievement. He is also an accomplished musician and nature photographer. We met at Cornell University, where Dr. Eisner is a professor and the Director of the Cornell Institute of Chemical Ecology.

When did you first become interested in science?

According to my parents, I got interested in insects when I could walk—and in chemistry at about the same time. My father was a chemist, and I share with him a sensitive nose and a memory for scents. I would know that my grandmother had visited the previous evening because I recognized the residual scent of her coat in the closet. So from an early age I've paid attention to the chemical images in the world around me.

A few years later, I actually did some experiments with insects—though without knowing what an experiment was. While I was growing up in Uruguay, we stored food in an ice box, and to keep the ants out, we would put little containers of turpentine around the legs of the box. My father had told me that turpentine was made from pine resin, and when I was about 10 it occurred to me that the resin might be a defense of the pine tree against insects. I was struck by the idea that plants might use chemical weaponry. To test my idea about pine resin, I streaked some across an ant trail—and found that the ants wouldn't cross it. But I didn't consider this science; to me it was just fooling around.

What happened after high school, when you came to the United States?

Soon after arriving, I volunteered to work at the American Museum of Natural History for a summer. The scientist I assisted, Charles Michener, encouraged me and gave me a list of books to read about insects. Then I had a setback: I was turned down by every college I applied to (including Cornell). I went to secretarial school for a few months, then got into Champlain College, a two-year college in Plattsburgh, New York. There I took a chemistry course that I liked a lot. But I also took a course in comparative anatomy, which was an eye opener. It taught me about evolution—for example, that you could relate the bones in the inner ear of a mammal to the jaws of a fish.

From Champlain College I transferred to Harvard, where after considering chemistry and medicine, I finally committed myself to biology. My entomology course as a senior and then meeting fellow student Ed Wilson [E. O. Wilson] during my first year of graduate school won me over completely. I remember thinking, how could I ever have considered being anything but a biologist!

What led you to chemical ecology?

My Ph. D. research was on the stomach of ants—how ants manage to save food for themselves and also for fellow ants. On the side, though, I was starting to collect and study insects that gave off all sorts of fascinating scents and stinks.

At that time, new discoveries in biology were laying the foundation for chemical ecology as a science. It was the heyday of insect hormones. The work on hormones, chemicals that act as signals within an organism, suggested to me that there might be chemicals that act as signalsbetween organisms. So when I arrived at Cornell for my first job, I went looking for a chemist I could work with who would be able to isolate and characterize the signal chemicals. I soon met Jerry Meinwald and started a collaboration that's lasted over 40 years.

It turns out that chemical signaling is ubiquitous. In fact, I've stopped thinking of air as air; I think of it as a carrier of messages. When I see a meadow filled with insects and other animals browsing on the vegetation, I think of the perfumes that attract pollinators to the flowers as well as the repellant chemicals that plants produce that discourage a butterfly from laying her eggs or a caterpillar from feeding on leaves. These repellant chemicals are a defensive strategy for the plant; the attractive floral scents are a reproductive strategy. Meanwhile, the insects are fighting with each other. The ants are repelled by substances produced by beetles. The beetles produce many of these chemicals because they've got a problem: They can't take to flight right away like a fly does; they have to unfold their wings first. They buy safety during that period with chemical weapons. Another insect, a moth, procures defensive substances from plants it eats as a caterpillar; later, as an adult, it bestows the chemicals on its own offspring. And these and many other insects use chemicals to attract mates. It's all chemical!

Does chemical communication go on in humans, too?

I think there is chemical signaling in humans, though not necessarily where you might expect it. Humans don't have a chemical that attracts males to ovulating females. On the contrary, the human female seems to be programmed to hide ovulation, chemically as well as anatomically. In this way, she induces the male—who can't be sure when she is fertile—to remain in attendance for long periods. (So what we call love has a subtle biological basis!) But there are clearly some kinds of chemical signaling going on between men and women. For instance, there are chemicals in the armpit of a male that when detected by a female can regularize her ovulatory cycling.

How do you choose subjects for research?

I'm an opportunist. I go out into the field and look around for something that catches my fancy. For example, I got interested in the bombardier beetle when I found some under a rock and picked one up. It made a popping sound, and a little puff of mist came out of its rear!

Is it true that you once put a bombardier beetle in your mouth?

Yes, I used to put insects in my mouth as a way of sensing their chemicals. With the bombardier beetle, I also sensed heat. I later learned that Charles Darwin may have had the same experience. In his autobiography, Darwin mentions something that happened while he was collecting beetles as a student at Cambridge University. One day he saw two beetles he wanted and grabbed one with each hand. But then he spotted a third interesting beetle. So, having only two hands like the rest of us, he popped one of the beetles into his mouth! Startled by a hot, irritating sensation, he spat out the one in his mouth and dropped the other two. I can't be certain that the one in his mouth was a bombardier beetle, but when I visited Darwin's home, I did see a bombardier in his insect collection, which goes back to his Cambridge days.

Tell us more about the bombardier beetle.

The bombardier beetle has an amazing defense system. When attacked, this animal generates a chemical explosion in less than 80 milliseconds and shoots chemicals out at 100°C, with an uncanny aim. If an ant is biting part of a leg, for example, the beetle hits that part of the leg, no matter what its position [see p. 26].

It took the contributions of a number of scientists to work out all the details. When I was first studying this beetle, I guessed from the smell that its spray contained chemicals called quinones. I wanted a way to make the spray pattern visible, and my father was able to tell me how to make a solution that would turn dark in the presence of quinones. I soaked a piece of filter paper with the solution and positioned the beetle on it. I then pinched one of the beetle's legs with forceps, heard the popping sound, and saw on the paper a clear pattern of the ejection. Soon after, a researcher in Germany identified the quinones in the beetle's spray and showed that the explosion is produced when the beetle mixes chemicals stored in two compartments of glands in its abdomen.

I then followed up on the physical characteristics of the spray in collaboration with several other scientists. One was Dan Aneshansley, an engineering student. Together we consulted physical chemists at Cornell, who calculated that the reaction of the chemicals in the beetle's glands should produce enough heat to raise the temperature of the spray to 100°C. We confirmed the prediction by rigging up an electronic setup to measure the temperature. Then we found evidence that the spray was pulsed, like the spray from a Water Pik but at a rate of 500 to 1000 pulses per second. With the help of Harold Edgerton of MIT, the inventor of the electronic flash, we were able to photograph the beetle in action. We used his high speed movie camera, shooting at 4,000 frames per second.

You've done a lot of work on behalf of the environment. What is your main focus?

Preservation of biodiversity—stopping the ongoing encroachment on nature. To me, science is like a three cornered hat. The first corner is obviously the discovery aspect, exploration. The second is the attempt to explain the findings and to relate them to other findings—to put together a view of the world. And the third corner is conservation.

You can argue that conservation is the ultimate purpose of it all. When you're doing science, you're trying to explain how you fit into nature and how nature operates around you. I feel that scientists—who all study nature in one way or another—have an obligation to be conservationists. I'm somewhat impatient with students who think of a scientific career that's totally insulated from activism.