Bombus muscorum (on the red list) Photo: Karin Ahrné, Swedish University of Agricultural Sciences
There are 274 species of bees in Sweden of which 37 species are bumble bees. Since they are enthusiastic flower visitors that need pollen and nectar to survive they are also important pollinators. Many species actively collect pollen from plants and thus carry large amounts of pollen between flowers. Bumble bees and honey bees are social and live in colonies, while other species are solitary. All bees are dependent on the availability of different resources within flight distance; flowers, nesting sites and for some species also building material. Bumble bees often build their nests in old mouse nests and other cavities in the ground, but some species prefer nesting higher for example the bumble bee Bombus hypnorum that nest in hollows in trees or nesting boxes for birds. Other bees dig their nests in sandy soils or use holes in wood, stems, housing walls or even empty shells. Several species use different types of building material to make cells for their offspring. Leaf cutter bees (Megachile) cover the walls in the cells with pieces of leaves while mason bees (e.g. Osmia bicornis) build with mud.
Bees often use man-made habitats and have historically used flower rich habitats in a small-scale agricultural landscape. Today the availability of these habitats decrease mainly due to changes in agricultural practices, but also because of urbanization. More than a third (98 species) of all bees in Sweden are Red Listed, which means that they are declining or expected to decline if nothing is done to avoid it. The main reason for the decline of bees is loss of habitat due to overgrowth and planting of trees in former flower rich grasslands and sandy soils. However, many species may utilize other man-made habitats such as embankments, sand- and gravel pits, flower rich road verges and different types of urban green areas that includes the resources they need. Close to 90 % (242 species) of all bees in Sweden can utilize urban habitats. For half of the species urban habitats are important while the other half can utilize urban habitats but depend more on other landscape types.