Changes in the biotope of the wart-biter (Decticus verrucivorus (L.)) in the Netherlands and Denmark (Orthoptera: Tettigoniidae)

Decticus verrucivorus has become rare in northwestern Europe. In Holland it is almost extinct now, but in Thy, a backward region in northern Denmark, the most important populations of the region occur. Causes of the decrease are new agricultural methods since the 1960’s, plantations of Pine woods on former heath and blowing sand areas and the ”management” of organisations for nature conservancy. In previous centuries human activities in dune and heath areas stimulated pioneer and transient plant communities. E.g. man cropped Heath, Marram Grass and wood from areas which have a status as nature reserve now. Herds of cattle cut off the vegetation for hundreds of years. After the acquisition of those semi-natural vegetations, being results of ”low energy” agriculture, the management policy of the State and of organisations for nature conservancy consisted of doing nothing, generally from the 1960’s onwards. Consequently succession of the vegetation took place during decennia, so that heath areas were overgrown with the grass Deschampsia flexuosa and the American tree Prunus serotina, while the dunes became covered with a uniform Marram Grass ( Ammophila arenaria) and Crowberry ( Empetrum nigrum) vegetation. Especially in The Netherlands these effects were intensified by lowering of the ground water levels, in some cases up to several metres, in combination with increased N-depositions. In The Netherlands projects of grazing management and controlled moving of the dunes have started. In Denmark, where the impoverishment of the system not yet has gone on so far, at the moment one is not inclined to take such measures. In the article photos and descriptions of a variety of habitats of D.v. with their Orthoptera faunas are given.