Even though dying bees under lime trees have been observed for over a hundred years, we still don’t fully understand this phenomenon. More work needs to be done to better understand the chemistry of nectar, pollen and odour, and its effects on bees. At Kew, we are working to address these questions. City trees provide us with important health benefits, such as filtering polluted air with their leaves. Some city trees are also abundant nectar and pollen sources for pollinators, a role that is often overlooked. To help maintain abundant and healthy pollinators, we need to better understand the positive and negative effects of the different, often non-native, trees we are planting in our cities.
Public interest in bees is intense. There’s rarely a week that goes by without a story in the press about populations plummeting. Although most of these stories focus on chemical pesticides, other factors may also be affecting bee survival. At Kew, we’ve been studying bees for years, and investigating how the plants they visit for nectar and pollen may play a part in their survival. Nectar and pollen are the main sources of protein, sugars and fats for bees, but these rewards that plants offer in return for the bee’s pollination service may contain other plant chemicals, some of which may be bioactive or toxic. We are particularly interested in these substances because while some may harm bees, others may be beneficial.
Plants produce toxins too
Bock, H. (1551). Kreüter Buch. Wendel Rihel, Strassburg.
Barlow, S.E., Wright, G.A., Ma, C., Barberis, M., Farrell, I.W., Marr, E.C., Brankin, A., Pavlik, B.M. & Stevenson, P.C. (2017). Distasteful nectar deters floral robbery. Current Biology. 27: 2552–2558.e3 Available online
Hauke Koch and Phil Stevenson investigate the theories behind the mysterious mass deaths of bees on lime trees, and other effects of pollen and nectar chemicals on pollinators.
This study was published recently in Biology Letters:
Small-leaved lime is an ancient-woodland indicator. If you spot it while you’re out exploring, it could be a sign you’re standing in a rare and special habitat.
Lime trees were often planted along roads by royal decree to get good luck in harvests.
Lime leaves are eaten by many species of caterpillar.
Credit: Blickwinkel / Alamy Stock Photo
A sign of ancient woodland
Other limes and hybrids. It is possible to tell true species apart by the underside of the leaf. Common lime (Tilia x europaea) has tufts of white hairs between the vein joints, whereas these are rusty red in small-leaved lime. Large-leaved lime (Tilia platyphyllos) has hairs all over the underside. Common lime is a hybrid and is rare in the wild in the UK.
Native to much of Europe and Britain it is found in woodland and grows best on moist but well-drained nutrient-rich soils.
Common name: small-leaved lime
Where to find small-leaved lime
Lime leaves are eaten by the caterpillars of many moth species, including the lime hawk, peppered, vapourer, triangle and scarce hook-tip moths. They are very attractive to aphids, providing a source of food for their predators, including hoverflies, ladybirds and many species of bird. The flowers provide nectar and pollen for insects, particularly bees, which also drink aphid honeydew from lime leaves.
Lime wood is soft and light, white-yellow and finely textured. It is easy to work and used in turnery, carving and furniture-making. Lime bark was traditionally used to make rope.