Whilst a good green roof designed for biodiversity will be attractive to many pollinators, providing nesting habitat is also an important consideration. Green roofs not only provide adequate forage for pollinators, but can also provide nesting for some species in the substrate. Tawny mining bees are known to mine nest holes in green roof substrate if it is relatively compact. Many interesting solitary bees however, do not nest in the ground. Providing habitat walls in the form of bee hotels is a relatively simple thing to do.
The largest bee hotel on a green roof
London has probably one of the largest bee hotels on a green roof in the world. On the roof of Lend Lease, the Australian Property developer, two huge walls overlook both an intensive roof garden and a green roof designed for biodiversity. Originally installed in 2009, within the first season, the bee hotels were being used by bees in the first year.
When we visited the roof in summer this year, the holes were filling up with nesting bees, particularly red mason bees, which are one of the commoner species in London.
Solitary Bees on green roofs
Another green roof designed for biodiversity in London has a smaller bee hotel. The habitat wall has 60 holes and this year 49 of these were in active use. Again the main residents were Red mason bees, although there appear to be a few leaf cutter bees make use of the smaller holes. In spring we managed to film the bees using the bee hotel. As the roof was not in full flower the bees were commuting from the ground. Obviously the bees were collecting pollen at ground level and returning to nest on the roof. Later in the year as the flowers on the roof bloomed, the bees made use of the green roof plants.
Today’s sponsored company can make bespoke bee hotels for green roofs. GreenRoofShelters always installs habitat walls on their products. This provides a full range of benefits for biodiversity – both nesting and foraging.