Photograph by Yadugiri V.T.

The documentary that we saw the day before yesterday - there were so many interesting experiments, like the one about the architecture of an ants' nest... Is there any one experiment that is your favourite?

Well, we succeeded to get an ant running on a treadmill. Initially we tried a lot; the ants moved around and didn't really run straight. Then we put these dots down which were sort of a landmark, and suddenly they were running straight. They needed an optical flow. And all this was in a cuvette to measure the oxygen consumption during the running, so we get an idea of the metabolism of the ant - we can measure how much energy they consume. This I like most, because it was the most difficult.

You started working in chemical ecology and ant biology about 50 years ago?

Let me see... I'm now 76, so... yeah that is true (laughs). Basically I started even earlier, but that's when I became more serious.

What changes do you see from when you started to now?

When I started, we had no idea that insects communicate by chemicals. There was not even a gas chromatograph invented, or mass spectrometer. I was so proud when I was a young assistant professor that I had my first gas chromatograph. All the methods I later used were not there when I started.

Sometimes, a major problem in developing nations is said to be the lack of resources...

What I always say to people in the so-called developing nations is, you are rich as a biologist. Your environments are full of interesting questions. First look out and see the questions. Sometimes, instrumentation can blind you because you are so impressed by it. My example is Karl von Frisch, my hero and my academic grandfather. Frisch won the Nobel Prize with the following equipment: a pencil, a notebook, a stopwatch, a compass. And he made earth-shaking discoveries - the waggle dance, the sun compass. My major criticism in my own home-town, in Germany, when they look for a new faculty member for example, is that again and again, the search committee does not ask 'What questions do you ask', but 'What methods do you know'. And they are so impressed by technology and machinery that they forget that the most important thing is the question - the scientific part.

Your research has both field and lab components. How do they interact with each other?

They are intricately connected. Usually after lab work, we go back to the field to test again. For example, there is an ant species of genus Messor, which sends out thousands of ants along a column to forage every morning. Interestingly, in the literature it has been said repeatedly that this has no chemical basis. But we saw very quickly in the lab that it did have a chemical basis - we now know which chemical and how much, we know the glands. Then I said it would be great if we could do it in the field. So we rolled out a long highway, a paper roll about 4m long, and with a syringe drew a line with the pheromones all the way out. And to our utmost surprise, the ants started to follow our trail along the paper highway (laughs).

That would look like magic!

But it took us quite a while. It sounds very easy now. We took a couple of detours. When you hear me talk, it sounds all so straightforward. This is always deceiving. If I would tell you how we came to do this experiment, it would be very boring for you (laughs).

Sometimes out of a mistake we get a new puzzle. We sent a compound from an ant of the genus Messor to our chemist, and he came back and said 'Oh, we got pyrazine'. Pyrazine is an aromatic organic compound which we had in the lab. We diluted it down to natural levels and tested it: the ants were running on it, and I said 'This is it, this is the trail pheromone', because I have never heard of an ant running on a substance they don't make. Then we made new samples and no one found pyrazine in it anymore; our first sample had a contamination. In subsequent work, we discovered another substance which is the real trail pheromone. But now comes the question: I said, 'Why is this ant running on pyrazine when it doesn't have it?' We haven't resolved this yet, but there is a hypothesis: there are many other Messor species, which do not have these huge columns, which are mostly individual foragers. Probably these have pyrazine. Column foraging may be a new evolutionary tool, and it could be that this one species still has the receptor system for pyrazine but does not make it any more. If we could show that the individual foragers use pyrazine, this would be a very interesting hypothesis. So, questioning again - I think that makes good science.

E. O. Wilson mentions in his book Naturalist that this sort of questioning led you to discover "wallpapering" in ants during your first field trip together in Costa Rica.

Exactly. You may have also read in Wilson's book - he's very charming, but he says that I sometimes drove him crazy (laughs). When we had one experiment and it worked, I said 'Well, but we need another experiment, you know', and after that he said 'Now it's done, and we can write a paper'. But Bert comes and says 'No, we need a third one' (laughs). [E O Wilson mentions in his autobiography, Naturalist, that Hölldobler is the only 'third-way researcher' he's ever known].

Ed and I are very complementary. My background is the experimental approach, and Ed comes from systematics. Ed is incredibly able to synthesise in a short time an unbelievable amount of literature. I read slow, but I read more accurately than Ed. Therefore for The Ants, we were very complementary. I think neither he nor I could have written The Ants alone. It was really an unusually lucky combination. [The Ants is a Pulitzer Prize winning book co-authored by Wilson and Hölldobler].

How important is documenting biodiversity, and what are the challenges in it?

I think it is extremely important. I don't know how India is equipped with natural history museums; they want to start a centre for chemical ecology here, you have butterfly work here... I think it would be unbelievably beneficial if they could also start a research museum somehow. It would stimulate a great deal of work. To know and preserve what is around you in the living world is extremely important. We talked about Ed Wilson - he's one of the major advocates of this. [The Museum of Comparative Zoology at Harvard University, of which Wilson is the Curator Emeritus, has, apart from other things, the world's largest collection of ants. The Encyclopedia of Life, which began in 2007 with the goal to provide 'a webpage for every species', is also Wilson's brainchild. These are just a couple of examples of Wilson's efforts towards documenting biodiversity.]

This is also what I say about human nature. Something we can celebrate lifelong is the diversity of life and the diversity of humans, the diversity of cultures. Every culture is worth preservation. Though I am a person who is outside of religion, I am interested in religious diversity. I see it more as a product of human invention, fantasy, to explain different things in the world. This is rich, there are many beautiful explanations. They are probably not right, but beautiful all the same. A world without diversity would be unbelievably boring.