Butterfly “Landkärtchen” is Insect of the Year

The spring generation of the map (left) differs significantly from the summer generation (right) © Senckenberg/ Wiemers, Schmitt

And the Oscar goes to... "Landkartchen"! The butterfly has been named insect of the year 2023 in Germany, Austria and Switzerland. This is to draw attention to the fact that the populations of this once common butterfly species are continuing to shrink due to drought and intensive agriculture. What a map looks like depends on the season in which it developed. The reasons for these seasonal differences are still unclear.

Since 1999, the Insect of the Year has been chosen by a jury of entomologists and representatives of scientific institutions. For the year 2023, they have now chosen the butterfly "Landkärtchen", which is the third butterfly overall to win the title.

Appearance varies depending on the season

A special feature of the maple (Araschnia levana), which is just four centimeters in size, is its pronounced “seasonal dimorphism”. This means that butterflies that develop in spring have a different color than those that only turn from caterpillars to butterflies in summer. The spring generation has orange wings with a black pattern, while the summer generation has black wings with a white pattern. In both cases, however, the pattern is reminiscent of the lines of a map, which is how the map got its name. Previous studies showed that wing color depends on how much sun the caterpillars get during the day. Long sunny days lead to the summer form and shorter, less bright days to the spring form.

"The decisive factors here are hormones from the group of ecdysteroids and the time at which they take effect in the pupa. The genes that control the release are regulated by the length of the day,” explains jury chairman Thomas Schmitt from the Senckenberg German Entomological Institute in Müncheberg. However, why the map is so seasonally dimorphic remains unclear. So far, neither clear indications of a camouflage nor a warning function of the different colors could be found. According to Schmitt, this uncertainty was one of the reasons why the choice fell on the small butterfly: "The map shows wonderfully that there is still a great deal of research to be done with widespread and supposedly well-known insects."

Indicator for ecologically intact cultural landscapes

But the map has more to offer than just its appearance. The insect also serves as an indicator of an ecologically intact cultural landscape. It only lays its eggs on the underside of stinging nettle leaves, which grow in moist areas such as stream and river valleys. The butterfly attaches its eggs to these in several short strings, which look like upturned turrets, glued to the underside of the leaves. This distinguishes this species from all other butterflies found in Europe. "But not every stinging nettle is good for the map," explains Josef Settele from the Helmholtz Center for Environmental Research (UFZ). “The eggs need high humidity for their successful development. For this reason, preference is given to plants that grow in damper places, such as in tall herb corridors in stream and river valleys.”

However, this pristine habitat is shrinking. "The stinging nettles, which are growing in large numbers due to the over-fertilization of the landscape, are therefore not automatically a good habitat for the map," says Settele. "The pronounced hot and dry summers of recent years have caused the populations of Araschnia levana to shrink significantly due to these habitat requirements." happen. The moths are also often encountered along sunny forest paths with a broad border of flowering plants.

"The map is an indicator of an ecologically intact cultural landscape, which is unfortunately becoming increasingly rare in Germany due to intensified agriculture, forest monocultures and the ever-increasing areas for settlement, industry and traffic," states Settele. That was another reason for drawing attention to the butterfly with its nomination as Insect of the Year.

Source: Senckenberg Research Institute and Natural History Museums

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