Mr. Hartmeyer, what actually fascinates you so much about carnivorous plants, which you also like to call "Fleischis"?
And: Do you have any favorites among the nearly 1,000 known species?

I am particularly interested in the highly effective animal traps of carnivorous plants, which give botanists and others the impression of ingenious evolutionary engineering, that is the biomechanics, or bionics for short. For example at the University of Freiburg studies snapping, catapulting or sucking carnivorous plant traps with latest analytical equipment, engineers are already transforming these into advanced and environmentally friendly practical applications. Studies of the mechanism of the Venus flytrap Dionaea muscipula, helped in the development of autonomously opening and closing sunshade lamellas for the shading of buildings and stadiums. They are operated without hinges, electricity or motors, using the mechanisms of the famous snap traps, the targeted use of inner tensions of the material. When you see such successes of bionics in practice, it is only then that one really understands what fascinating mechanisms evolution has produced with the carnivore traps.

Even the well-known German science journalist Volker Arzt asked by e-mail whether he could show the pictures of the fly-slinging predatory plant, taken in our living room, for the first time on television in the program "Planet Wissen". Of course, we gladly agreed. The report was broadcast in 2015 and online until the end of 2020.

From when were carnivores actually described scientifically?

Carnivorous plants were first scientifically described in the 18th century, not infrequently by the famous Carl von Linné, the inventor of binary nomenclature, with the help of which science can name all living beings by means of a genus and species name. However, even at that time, he generally rejected the assumption that these plants were carnivorous, i.e. they deliberately ate animals. He probably feared trouble from religious authorities for such claims, similar to those experienced 100 years later by Charles Darwin for suggesting carnivorous plants.

For Darwin this criticism was not less massive than for his theory of evolution published 16 years before. In 1875 Darwin published his famous experiments with sundew, etc. the first scientific book, "Insectivorous Plants" in which, as the title suggests, he clearly writes about insectivorous plants. Evangelical fanatics saw the "divine order" endangered if plants were to eat animals instead of the other way around.

Today, it is scientifically undisputed that carnivores capture insects and digest them with enzymes, so Darwin was right. We were even able to clearly prove in experiments that some sundew species already starve to death as seedlings if they cannot catch enough food.

How does one get an invitation to Japan, for example, with such a hobby?

For the answer I must go a little further. Irmgard and I spent since 1990 on three carefully prepared trips totaling of more than seven months in Australia, where most species of carnivorous plants exist. The motto for us was always "Take only photos, leave only footprints". With small airplanes, helicopters and cross-country vehicles we searched and filmed carnivores and a phenomena associated with them, sometimes accompanied by local experts, but mostly as a team of two. We observed symbioses between carnivorous plants and predatory bugs (Cyrtopeltis & Bybliphilus), which can live completely unharmed and mutually beneficial in the midst of the glue traps . In "Down Under", until our publication in an Australian journal in 1996, such symbioses/mutualisms were only known from a rather limited region about 3000 km south around the city of Perth.

In addition to our private investments in adventurous excursions and better film equipment we had a good portion of luck. Irmgard and I actually managed to film several undescribed symbiosis/mutualisms in northern Australia. As the icing on the cake, we found an undescribed sundew in 1995, whose transformed "tentacles" (emergences) reflect yellow light.

This was new in the genus Drosera. In 2001, after this plant suddenly appeared in Germany, we showed it to the biochemist and systematist Dr. Jan Schlauer, who was really electrified by our find and immediately started the scientific description of the new species. The reflective emergences of "our" sundew and the newly found symbioses caused a worldwide attention in expert circles. Nevertheless, I was astonished when suddenly the letter of a Prof. Kondo from Hiroshima University arrived with the words: "I would like to invite you to show a film lecture about your discoveries in Australia in the context of the International Carnivorous Plant Conference 2002 at the Natural History Museum in Tokyo. In addition, I would be pleased if you could produce an official video about the conference." This was such a great honor for us that we immediately booked the flights. The conference in English was a great success, which brought us many new worldwide contacts, friendships and follow-up invitations.

Have you also experienced bizarre surprises in the greenhouse?

Oh yes, our mouse-eating pitcher plants Nepenthes come to mind. Small vertebrates have been found in large pitchers in Borneo, but it was surprising in our greenhouse. A total of five mice were caught by two large plants in a few years, so this was not a one-time fluke. We would never feed vertebrates to plants! 

The mice came in unwanted, and we always noticed it only by the typical stench near the trap, when digestion had already started. In fact, the pitchers function like a real stomach with digestive enzymes. For us of course it was an ideal opportunity to investigate how the plant does this and what remains from such large prey.

The following probably took place: Attracted by the sugar-containing excretions, which are produced by the nectar glands on the underside of the lid, the mouse climbs up the rough outer surface of the pitcher onto the sturdy "collar", the peristome, which surrounds the opening. There it must stand up on two legs and bend slightly forward to lick the sweet drops under the lid above her. Thereby a careless movement is enough, the rest is done by gravity. The victim falls into the digestive fluid and drowns without any chance of climbing the very smooth inner walls. Since all pitchers remained completely undamaged after the capture, it was a proof that there was no possibility for the rodents to bite through the walls.

The digestion of an adult mouse takes about six weeks. When the trap was cut open, the remains were completely flattened and seemed almost grown into the wall. So robust is the lower part of the pitcher that it needed to be cut with a scalpel to remove the remains. Remaining were the fur, hairs and gnawing teeth, as well as small remains of the most massive bones. The rest of the body had been digested with enzymes and absorbed. The latter could be seen by the fact that the following pitchers of the plant grew even larger and stronger. As macabre as the pictures may be, our somewhat bizarre article with the photos found great interest. Translations appeared in several countries; even a large Indonesian garden magazine (Trubus) printed a report on it.

Less bizarre, even dangerous turned out to be captures in the greenhouse of the tropical tiger mosquito Aedes aegypti, which immigrated only a few years ago, and which we discovered in the glue of our sundews. They transmit dangerous diseases such as Zika, Chikungunya and dengue fever. The Weiler Public Order Office had asked citizens to report findings of the mosquitoes. They immediately sent a biologist to us, who confirmed that they were indeed the tropical bloodsuckers. He gave me Culinex tablets, with Bacillus thuringiensis israelensis with which the old branches of the Upper Rhine Valley are treated every spring. It is only deadly for mosquito larvae. One hundred years ago, our region was still a malaria area due to its mild climate and the transmitting Anopheles mosquitoes are still present. A broth from the tablets is then given into the water bowls in which our carnivores are standing, which are unfortunately also ideal breeding sites for the invasive tiger mosquitoes. The control is supported by our numerous sundew species in the greenhouse, for which all the mosquitoes are ideal prey.

Photo: Hunting for dangerous tiger mosquitoes Aedes aegyptii, these Drosera serpens (left) and Drosera paradoxa
(both Australia) were successful in the greenhouse. This also helped to clearly identify the mosquitoes.

Are you still currently involved in scientific projects on carnivorous plants?

This hobby has never been and will never be boring. Since 2016 we have been cultivating certain sundew species in order to examine them for their chemical constituents in collaboration with Dr. Jan Schlauer. The so-called chemotaxonomy is quite helpful for both systematics and questions about the evolution of the genus. Up to 2019, this resulted in several scientific publications. All these articles can be found on our homepage.

Only last year, together with Prof. Stephen Williams (USA), we were able to publish an article about experiments with ants in our garden, which happened to have made a burrow right next to a group of Venus flytraps and really walked permanently through the traps without triggering them - A great coincidence. We succeeded in proving statistically that the large snap traps allow small ants, which are unprofitable as prey, to escape in a targeted manner by combining several ingenious features in order to save energy. Of course, we have films of this, which can be seen on our YouTube channel. In the meantime, more than 1.6 million views prove that they are of interest.

But one more point on your question: Fortunately - you will have guessed it - even during this interview, some laboratory equipment runs analyzing our plant samples taken in 2020. Sown in April, we harvested them at the beginning of October in the greenhouse and sent them by express to a laboratory in Helsinki. It looks quite good so far; a new publication will be released in 2021 at the latest, depending on the duration of the peer reviews it will appear in a specialist journal.

Recently, we were surprised to receive an e-mail from Dr. Poppinga from the University of Freiburg with great news: The aforementioned catapult-flypaper trap has now been entered into the Guinness Book of Records as the "fastest terrestrial predatory plant in the world" with 75 thousandths of a second (ms) for a capture process, based on our joint laboratory measurements.

Six years ago you combined a vacation in the Harz mountains with some excursions through our Brocken moors. Accompanied by Brocken gardener Dr. Gunter Karste, you were able to examine the sundew deposits there. You published your results in a very interesting and not less entertaining video. Is there perhaps the intention to repeat such an action again?

I have the best memories of the excursions with Dr. Gunter Karste on the Brocken and surroundings. We saw, for the first time butterworts (Pinguicula), sundew as well as some orchids (Dactylorhiza species) at natural places in my old homeland. This was a great experience, especially because the fascination for carnivorous plants in me was actually caused by the round-leaved sundew D. rotundifolia.

I am still happy like crazy when I see this plant in the nature in front of my camera. In addition there is also scientific interest. As the only one of our native sundew species, D. rotundifolia forms at different times either glue tentacles or completely dry snap tentacles, similar to the ones of the Australian catapult traps, although not quite as fast moving. Why there is this dimorphism here and what causes the formation of the different tentacles in this species, I have not yet been able to explain. I hope that it will happen one day. Our film “Fleischfresser auf dem Blocksberg” (Translated "Carnivores on the Blocksberg"), which also deals with our family history in Benneckenstein, can be watched free of charge on our YouTube channel.

We have considered further excursions in the Brocken area a few times since then. At the moment, however, we can't travel with my 89-year-old mother, who of course always accompanied us to Benneckenstein. For health reasons we do not want to leave her alone for a long period in Corona times. I am sure that we will go on tour in the Harz mountains again in the future and we are looking forward to it!