Het bijenrijk van het Tolkamerdijkje

The small nature reserve of Tolkamer-dijkje (5 ha) is situated within the floodplains of the Rhine river near the village Tolkamer. It consists of a central low lying area, enclosed by two dykes: an old summer levee and a more recently built one. Nearby there is a sandy terrain called the “Helicopterveldje” and harbor facilities. The area consists of one of the very few locations in Holland with a well-developed dry river grassland vegetation (Medicagini-Avenetum pubescentis and different types of Arrhentheretum elatiors). We visited the area frequently between 2001 and 2009 to make an inventory of the bee and wasp fauna. A total number of 82 species of bees (21 Red list species) and 43 species of wasps were recorded. Most of these species build their nest in the ground or in holes. The number of oligolectic bees is high, but some expected species are absent. The number of parasitic bees is high. The number of wasps is extremely low. Comparing Tolkamerdijkje to other floodplains within the Dutch Rhine, we can say that it has a characteristic species composition. The percentage of shared species (Σ common species area A and B/ Σ species area A * 100 %) amongst other well-investigated floodplains (Millingerwaard, Meinerswijk) is the lowest of all. Another conclusion is that the species pool in some other areas are probably under-examined. So there is still much to explore and to discover in the riverine landscape.