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. Wild bees, however, were not the main focus of the study but provided important data.
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 | April | May | June | July | August | September | ||
| Apis mellifera | x | x | x | x | x | x | ||
| Bombus terrestris (buff tailed) | x | |||||||
| Bombus lucorum (white tail) | x | |||||||
| ⬇︎ Plant Species used by bees on site | April | May | June | July | August | September | ||
| Echium vulgare | x | x | x | x | x | x | ||
| Linaria repens | x | x | x | x | x | x | ||
| Laban - Lewisham | ||||||||
|---|---|---|---|---|---|---|---|---|
| ⬇︎ Species | April | May | June | July | August | September | ||
| Apis mellifera | x | x | x | x | x | |||
| Bombus terrestris (buff tailed) | x | |||||||
| Bombus pratorum (early) | x | |||||||
| Bombus pascuorum (common carder) | x | x | x 15+ | x | x | |||
| Bombus lucorum (white tail) | x | x | ||||||
| Bombus lapidarius (red tail) | x | x! | x 15+ | |||||
| Moth small brown | x | |||||||
| Cinnabar moth | x | |||||||
| ⬇︎ Plant Species used by bees on site | April | May | June | July | August | September | ||
| Echium vulgare | x | x | x | x | x | |||
| Trifolium pratense | x | x | x | |||||
| Trifolium medium | x | x | x | |||||
| Anthyllis vulneraria | x | x | x | |||||
| Papaver rhoeas | x | x | ||||||
| Lotus corniculatus | x | x | ||||||
| Trifolium arvense | x | x | ||||||
| Sedum album | x | |||||||
| Regent's Park - London Zoo | ||||||||
|---|---|---|---|---|---|---|---|---|
| ⬇︎ Species | April | May | June | July | August | September | ||
| Apis mellifera | ||||||||
| Bombus terrestris (buff tailed) | ||||||||
| Bombus pratorum (early) | x | |||||||
| Bombus pascuorum (common carder) | x | x | ||||||
| Bombus lucorum (white tail) | x | |||||||
| Bombus lapidarius (red tail) | ||||||||
| Bombus hortorum (garden) | ||||||||
| Grasshopper | x | |||||||
| ⬇︎ Plant Species used by bees on site | April | May | June | July | August | September | ||
| Anthyllis vulneraria | x | x | ||||||
| Plantago media | x | |||||||
| Leucanthemum vulgare | x | |||||||
| Sedum album | x | |||||||
| B1 - Canary Wharf | ||||||||
|---|---|---|---|---|---|---|---|---|
| ⬇︎ Species | April | May | June | July | August | September | ||
| Apis mellifera | x | |||||||
| Bombus terrestris (buff tailed) | x | x | x | |||||
| Bombus pratorum (early) | x | x 2+ | ||||||
| Bombus pascuorum (common carder) | x | x | x | x | ||||
| Bombus lucorum (white tail) | x | x | ||||||
| Bombus lapidarius (red tail) | x | x | ||||||
| Bombus hortorum (garden) | ||||||||
| Icheneous | x | |||||||
| Autographa gamma (Silver y moth) | x | |||||||
| Grasshopper | x | |||||||
| ⬇︎ Plant Species used by bees on site | April | May | June | July | August | September | ||
| Echium vulgare | x | x | ||||||
| Clinopodium vulgare | ||||||||
| Trifolium medium | x | |||||||
| Anthyllis vulneraria | x | x | x | |||||
| Sonchus arvensis | x | x | ||||||
| Leucanthemum vulgare | x | |||||||
| Centaurea cyanus | x | |||||||
| Sedum reflexum | ||||||||
| Prunella vulgaris | x | x | ||||||
| Trifolium arvense | x | x | ||||||
| Plantago media | x | x | ||||||
| Anthemis arvensis | x | x | ||||||
| Sedum album | x | |||||||
| Malva moschata | x | |||||||
| Silene dioica | x | |||||||
| Clinopodium vulgare | x | |||||||
| Daucus carota | x | |||||||
| Knapweed | x | |||||||
| FC4 - Canary Wharf | ||||||||
|---|---|---|---|---|---|---|---|---|
| ⬇︎ Species | April | May | June | July | August | September | ||
| 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 sp | x | |||||||
| ⬇︎ Plant Species used by bees on site | April | May | June | July | August | September | ||
| Allium schoenoprasum | x | x | ||||||
| Petrorhagia saxifraga | x | x | ||||||
| Sedum reflexum | x | |||||||
| Sedum album | x | x | ||||||
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.
Green roofs and Bees around the world
Since we originally wrote this article, a number of other studies have taken place around the world. Firstly a study in Vienna concludes that wildflowers are important for bees too. Roofs with sedum only are less beneficial for wild bees than ones with wildflowers. The UK and CH studies are also mentioned in a global study of green roofs and wild bee research. The paper concludes that there is relatively little research, compared to physical science studies on the subject. This means that the UK and CH studies are still seminal pieces of research.