Wat is er aan de hand met het Hooibeestje?

Coenonympha pamphilus is a common butterfly In the Netherlands. The numbers of this species are decreasing however, and monitoring surveys since 1990 have indicated that the decline is more significant in rural areas than In the dunes. A sudden decline of the butterfly numbers in the spring of 1991 was presumably caused by ground-frost which followed a period of warm weather, killing many of the pupae. The butterfly populations were able to recover in the dunes but not in the rural areas. The reason for this can only be speculated on.