Arthropod richness in roadside verges in the Netherlands

Urbanisation and intensifi cation of agriculture has led to large scale destruction of natural and seminatural areas in Western Europe. Consequentially, the conservation of biodiversity in small landscape units has become a matter of increasing urgency. In this paper, we inventoried the arthropod diversity in roadside verges in the Netherlands and studied the relative importance of these linear elements. In addition, the occurrence of arthropods in roadside verges in other countries was studied by literature research. In the period 1998-2008, we sampled 57 roadside verges. Th is was mainly done by pitfall trapping, using sweeping nets and insect nets, and by sight observations. For several arthropod groups the majority of the Dutch indigenous species was sampled: ants (56% of the indigenous species), grasshoppers (53%), harvestmen (67%) and two spider families (52% and 68%). For ground beetles, weevils, butterfl ies, bees, hoverfl ies and three other spider families, values between 18-41% were found. Considering that only a minute fraction of the vast network of roadsides was sampled, these fi gures are remarkably high. Roadside verges are occasionally reported to act as dispersal corridors for exotic species, but this could not be confi rmed for arthropods in the Netherlands. Several of the arthropod species inventoried in the Dutch verges are classifi ed as threatened: fi ve grasshopper and eleven bee species appear on national Red Lists and six ant species on the IUCN Red List. Also, in several other countries roadside verges in intensively used landscapes appear to off er opportunities for arthropod conservation. We conclude that, if rightly managed, roadside verges can serve as an important and valuable arthropod habitat. Th erefore, we strongly recommend taking always into account the conservation of these arthropod assemblages during planning and actual management of roadside verges