Danube clouded yellow (Colias myrmidone) once was a regular inhabitant of Serbia, while today the only evidence of its presence are old scientific publications and a few dusty individuals in valuable collections of the natural history museums. Judging by the maps, it seems that the butterfly was distributed along the Danube and in the valleys of other large rivers. Since it is most likely that we’ll never know where this clouded yellow really lived, we can only guess. Its tight connection with the rivers can be explained by the butterfly’s appearence in the lower altitudes, but its disappearance from this region is still a mystery.
And this happened everywhere! The butterfly went extinct in a few decades in most of Europe, getting higher threat status and legal protection. Despite this, the scientists still didn’t agree about the real cause for disappearance of this species from Europe. Some hypothesis have said that the butterfly occupied Europe relatively recently from Asia and it simply retreat with the arrival of somewhat unfavourable conditions. One of the very probable explanation lies in the agricultural changes, where meadows were either left to became overgrow in forests or became plugged for agricultural fields. Still, the meadows with plants from genus Chamaecytisus, where the caterpillars of the Danube clouded yellow are feeding, are still found across the Balkans. Negative effect of humans could hardly explain simultaneous disappearance of the butterflies from so many countries, where agricultural practices are usually very different. And the true is maybe somewhere in between. Maybe joint effect of all this circumstances could lead to the vanishing of the butterfly in our country.
But still, the butterfly did not just simply disappear everywhere. It remained on a several locations in a few countries, among which the most bright example is Romania. Maybe it’s also realistic to expect this butterfly in Serbia? However, after a few unsuccessful searches for the Danube clouded yellow in Serbia, this time we decided to begin our search from Romania. Our friends Czaba and Agnesh, along with their professors and a team of volunteers, has bean marking this butterfly in locality called Agârbiciu and we decided to join them. This was a great chance to see one of the last populations of the Danube clouded yellow in Europe and to learn something more about the places that this butterfly inhabits.
The first thing that crossed our minds was the locality itself. Agârbiciu is a hilly area that has bean managed by cows, leaving the host plants for the caterpillars ungrazed. And there were a lot of plants from the genus Chamaecytisus, although it seems that the butterflies are feeding only on Chamaecytisus triflorus. Another uncommon observation were the places where this butterfly occurs. If we take a look at all the localities in Romania, we can see that they are situated in about 500 meters above sea level, but are also somewhat more to the north. In fact, the locality irresistible resembles the area of Vlasina (1300 m), where the Balkan clouded yellow (Colias caucasica) can be found in Serbia. The Balkan clouded yellow is the closest relative to the Danube clouded yellow and is considered as the mountain species, never observed on the lower altitudes. I asked myself if it is possible that the Danube clouded yellow remained only on the higher altitudes because of the climate changes or a few unfavourably hot years? This could explain its massive extinction through the Balkans.
With this idea we went back to Serbia. But we were not quite finished with Romania, since on our way back a new population of the Danube clouded yellow has bean discovered close to Mănăstireni. Having some experience from Romania, we have chosen potential localities in Serbia where butterfly habitats were on a bit higher elevation. The first on the way were the habitats surrounding Vršac mountains. Here we had great help from Zoran Gavrilović, a great biodiversity expert for Vršac and its surroundings. But there was no trace of our butterflies! We managed to record a lot of other species, find a meadows with Chamaecytisus sp. and visit great habitats that represent real centres of biodiversity in Panonia. Although we would like to stay more in Vršac hills, we had to move on. The next localities were in Đerdap, where the managers of the protected area PE „Nacional Park Đerdap“, recommended us to visit hilly areas on Miroč. Everything was perfect, there was a lot of Chamaecytisus sp. and apparently there were real habitats for the Danube clouded yellow. But still, the butterfly was not found once again.
The plants used to feed caterpillars of this species are found everywhere, from the flat Vojvodina to the hilly Stara planina. And as long as the plant is present, there is a chance that the butterfly remained hidden on some small habitat where our foot have never approached. And it is waiting to be recorded once again by some kind visitor.
Text: Miloš Popović