Bees and Green Roofs – studies in London and Switzerland

Bees are known to use green roofs and images of them are often used in green roof company literature.  Hymentora were collected as a by-product during a London PhD ‘Green roofs and invertebrate biodiversity’ research project. They were not the main focus of the study but provided important data.

bees on green roofs
Colletes species on an intensive green roof

 

Bees are known to use green roofs and images of them are often used in green roof company literature.  They were collected as a by-product during the London PhD ‘Green roofs and invertebrate biodiversity’. They were not the main focus of the study but provided important data.

A study of bees on green roofs in Switzerland showed that roofs planted with a mix of both wildflowers and sedums were used throughout the foraging season [April to September], whilst roofs merely planted with sedums were only visited by bumblebees during June/July, when sedum species were in flower. The full research paper is available to download. 924.64 Kb

The Swiss study recorded 77 different bee species, of which 54 occur in the UK. Of the 54 species,  21 were recorded during the long-term study of green roofs and invertebrate biodiversity in London.

Green Roofs for Foraging Pollinators

Hymenoptera collect pollen for larval food and the adults feed on nectar. Certain species gather food from single species of flower (monolectic), whilst others feed on closely related flowers (oligolectic). Long-tongued bees, such as leaf-cutter and some species of bumblebees collect nectar from labiates and leguminous flowers, whilst short-tongued species, such as Colletes visit flowers from the daisy family. Other short tongues species tend to visit flowers with short corolla such as Rosaceae, Asteraceae and Apiaceae.

Biodiverse green roofs, with a wide range of wildflowers,  are therefore perfect for many foraging bees. It is also crucial for bees to find suitable foraging sites from early spring to late summer. Therefore green roofs  that are planted with a wide selection of wildflowers and sedums can provide an important forage habitat for bees in urban environments.

They also frequently use moss as a drinking source even where water is readily available. Mosses are relatively common on most green roofs.

Below is a series of tables of several green roofs in London where certain bee species were observed during 2009. A further table provides a list of plants the bees were observed to be foraging on.

Bees and Green Roofs

Roots and Shoots - Lambeth
⬇︎ Species AprilMayJuneJulyAugustSeptember
Apis melliferaxxxxxx
Bombus terrestris (buff tailed)x
Bombus lucorum (white tail)x
⬇︎ Plant Species used by bees on siteAprilMayJuneJulyAugustSeptember
Echium vulgarexxxxxx
Linaria repensxxxxxx
Laban - Lewisham
⬇︎ Species AprilMayJuneJulyAugustSeptember
Apis melliferaxxxxx
Bombus terrestris (buff tailed)x
Bombus pratorum (early)x
Bombus pascuorum (common carder)xxx 15+xx
Bombus lucorum (white tail)xx
Bombus lapidarius (red tail)xx!x 15+
Moth small brownx
Cinnabar mothx
⬇︎ Plant Species used by bees on siteAprilMayJuneJulyAugustSeptember
Echium vulgarexxxxx
Trifolium pratensexxx
Trifolium mediumxxx
Anthyllis vulnerariaxxx
Papaver rhoeasxx
Lotus corniculatusxx
Trifolium arvensexx
Sedum albumx
Regent's Park - London Zoo
⬇︎ Species AprilMayJuneJulyAugustSeptember
Apis mellifera
Bombus terrestris (buff tailed)
Bombus pratorum (early)x
Bombus pascuorum (common carder)xx
Bombus lucorum (white tail)x
Bombus lapidarius (red tail)
Bombus hortorum (garden)
Grasshopperx
⬇︎ Plant Species used by bees on siteAprilMayJuneJulyAugustSeptember
Anthyllis vulnerariaxx
Plantago mediax
Leucanthemum vulgarex
Sedum albumx
B1 - Canary Wharf
⬇︎ Species AprilMayJuneJulyAugustSeptember
Apis melliferax
Bombus terrestris (buff tailed)xxx
Bombus pratorum (early)xx 2+
Bombus pascuorum (common carder)xxxx
Bombus lucorum (white tail)xx
Bombus lapidarius (red tail)xx
Bombus hortorum (garden)
Icheneousx
Autographa gamma (Silver y moth)x
Grasshopperx
⬇︎ Plant Species used by bees on siteAprilMayJuneJulyAugustSeptember
Echium vulgarexx
Clinopodium vulgare
Trifolium mediumx
Anthyllis vulnerariaxxx
Sonchus arvensisxx
Leucanthemum vulgarex
Centaurea cyanusx
Sedum reflexum
Prunella vulgarisxx
Trifolium arvensexx
Plantago mediaxx
Anthemis arvensisxx
Sedum albumx
Malva moschatax
Silene dioicax
Clinopodium vulgarex
Daucus carotax
Knapweedx
FC4 - Canary Wharf
⬇︎ Species AprilMayJuneJulyAugustSeptember
Apis mellifera
Bombus terrestris (buff tailed)
Bombus pratorum (early)x
Bombus pascuorum (common carder)
Bombus lucorum (white tail)
Bombus lapidarius (red tail)x
Bombus hortorum (garden)
Megachile spx
⬇︎ Plant Species used by bees on siteAprilMayJuneJulyAugustSeptember
Allium schoenoprasumxx
Petrorhagia saxifragaxx
Sedum reflexumx
Sedum albumxx

From these studies green roofs provide a good forage source for bees in the urban environment. Roofs with only sedum are not as attractive throughout the season. It is  imperative  therefore that mix of both sedums and wildflowers are used to maximise the benefit to pollinators.

Written By Dr. G. Kadas And Dusty Gedge