Insect of the Year

Since the "Insect of the Year" board of trustees was established in 1999 – primarily by the then director of the German Entomological Institute, Prof. Dr. Holger Dathe – this commission selects each year an insect species that should enjoy greater fame because of its special importance for the ecosystem, its particular rarity, its aesthetic value or even its "ordinariness".

The Insect of the Year is intended to bring an exemplary species (and insects in general) closer to people. Well-known entomologists, representatives of research institutions and nature conservation organisations from Germany, Austria and Switzerland together make an important and difficult decision, the choice among about one million described insect species (even if "only" about 35,000 of them occur in Germany) and select the species that is to represent the inconspicuous and yet so important "creepy-crawlies" among humans for a whole year.

Insect of the year 2023: The Map

The underside of their wings gave the species its common name. © Thomas Schmitt

The map (Araschnia levana) amazes with its variable appearance: The spring generation has an orange ground colour with black markings. The summer generation, on the other hand, is predominantly black with a curved white band on the forewing and hindwing. Common to both generations is a relatively colourful underside of the wings with numerous lines of varying thickness. This is reminiscent of a map, which gave the species its common name.

In extensive laboratory experiments, it was proven more than half a century ago that caterpillars of the map that grow under long-day conditions - with more than 15 to 17 hours of light - develop into moths of the summer form without a resting phase. If the caterpillars develop during shorter, less bright days, they always take a break and form the spring generation after hibernation.

The summer generation of the Map is predominantly black with a curved white band on the forewing and hindwing. © Thomas Schmitt

If caterpillars grow in conditions that lie between the two forms, an early autumn generation develops with a wing pattern that lies between the other two forms if the environment is sufficiently warm. Hormones from the ecdysteroid group and the time of their action in the moth pupa are decisive for this. The genes that control the secretion are regulated by the length of the day. An early release of the hormones leads to the formation of the summer form.

But what is the purpose of the different colour variants? Does the orange form, in contrast to the summer form, represent a warning colouration? Or does this form enjoy better camouflage in spring on the leaf-covered ground at the edge of the forest, while the chocolate-brown form is better protected from predators in summer conditions with the then stronger light contrasts? An experiment with blue tits showed that none of these assumptions can be confirmed. While the physiological control of the development of the land carpenter is already quite well studied, the evolutionary reasons for this seasonal dimorphism remain unsolved.

The Map attaches its eggs in several short strings to the underside of leaves of the stinging nettle (Urtica dioica). © Thomas Schmitt

The egg-laying of the Map is also remarkable: it attaches its eggs in several short strings to the underside of leaves of the stinging nettle (Urtica dioica). This distinguishes the species from all other butterflies found in Europe. The eggs need high humidity for successful development. Preference is therefore given to plants that grow in damp places, for example in high herbaceous vegetation in stream and river valleys. The stinging nettles that grow in large numbers due to the over-fertilisation of the landscape are therefore not automatically a good habitat for the land hawkweed. The pronounced hot and dry summers of the past years caused the populations of Araschnia levana to shrink considerably due to these habitat requirements.

In well-structured landscapes with hedges, bushes, flowering meadows and near-natural forest and watercourse edges, however, the Map can still be quite numerous. The butterflies are also often found 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 rarer and rarer in Germany due to the intensification of agriculture, forestry monocultures and the ever-increasing settlement, industrial and traffic areas.