Estimation of Western Europe number of bee species varies between 2000 and 4500 (Williams 1995) but there are substantial indications of a decline in bee species in Europe and other regions. In Denmark, wild bee species richness, distribution, and abundance have not been studied in detail for about 75 years, and nothing is known about which species are potentially vulnerable or endangered. A rough estimate of solitary bees and bumblebees includes approximately 238 species (26 genera) and 29 species respectively. In a pan-trap survey of six kilometres of semi-natural habitats in a Danish agricultural landscape, 72 solitary bee species and 19 species of bumblebees were recorded, several of which are considered vulnerable or endangered in neighbouring countries. Nesting conditions for rare cavity-nesting species and the possible role of the semi-natural habitats as corridors for species dispersal are discussed. A new group of non-parametric species richness estimators, supplied by the free-ware programme EstimateS 5 (Colwell 1997), was used to estimate true species richness in the area of study and an additional 23 potential species was depicted from abundance and distribution of the 91 recorded species. Efficiency of window-traps in yellow pan-traps for bee fauna surveys is evaluated and is found to be an efficient method for investigations of species richness and relative abundance of bees.