Updated: 15th March 2023
Whilst some lime trees (Linden) are toxic for bees, others provide a very useful nectar source.
Reputedly, there are limes (Tilia) which can be foraged on safely by some bee species, whilst they are poisonous for others, or have at least a narcotic/sedative effect.
Bees vulnerable to the sedative characteristics of certain lime trees will obviously be at risk of attack by predators.
If you find dead bees beneath a lime tree, suffice to say, it’s likely you have a poisonous variety, or at least one which has those narcotic effects.
An exception to this could be cases where dead bumble bees have been found beneath a lime tree with parts of the head or abdomen missing.
It is known that Great Tits in particular, will sometimes predate on bumble bees feeding on limes, and will eat the parts of the bumble bee they apparently find most appetizing! This phenomenon can also occur in other settings.
Some lime trees are favoured by beekeepers, and Linden honey is especially popular in Romania, for example.
Bees may also harvest the honeydew produced by aphids on the leaves.
is thought that non-toxic limes are:
Bumble bees are thought to be particularly vulnerable to certain Limes.
The following lime trees are regarded as poisonous for bees (or having an unfortunate narcotic effect), and so should be kept out of the bee garden.
Lime trees are said to have a short flowering season.
If you are considering buying lime trees, consider Tilia platyphyllos or Tilia cordata, since it
is generally considered that both of these species of lime trees are safe for foraging
bees. However, space may be an issue!
However I am not even sure it is worth taking a risk with any lime trees in the garden, given that many beautiful flowering trees and shrubs are available.
This is as yet unclear. Various theories have been proposed, and later 'debunked' such as mannose content in nectar being responsible1.
Another theory was that some bumble bees simply starve themselves to death by remaining 'loyal' to lime tree nectar (known as 'high nectar resource fidelity'), so that they continue to forage even when the lime tree has stopped producing nectar. It was proposed that the bees then run out of energy and die from starvation before returning back to the nest, but this theory has also been questioned2.
If the theory were correct, why would they not run out of energy when foraging at other plants, and why is it particular to some lime species?
Other research throws doubt on these ideas and it is also suggested that bumble bees are calculated in their assessment of nectar rewards1,3.
A further theory was that deaths in bumble bees occur due to the combination of a low temperature of <30°C and nectar volume, resource fidelity, and alkaloids in nectar1.
However, the authors of the study had already noted that resource fidelity is questionable. Furthermore, are Linden trees really blossoming during dangerously cool temperatures for bumble bees, given that even Tilia tormentosa generally blossoms from June to July? From research I have seen, about 80% of bumble bees in the sample survived after exposure to −5°C for 2 hours4 and bumble bees are fine at temperatures of 15°C.
Previously, I had referred to the effects of drowsiness causing some bees to be vulnerable. I then changed this to accommodate the theory of the founder of toxicology, Paracelsus, which is: "The dose makes the poison".
Having reconsidered, I am reverting back to the original observations from Goulson's book above, and also those originally posted by Kew Gardens prior to the publishing of various studies.
It seems to me that comparisons and investigation of the narcotic effects of nectar in Tilia species merits further investigation.
Effects of 'drowsiness' would explain why some bumble bees are found crawling beneath the trees, whilst others are dead.
Moreover, there may be subtle considerations for researchers.
It appears that dead honey bees are infrequently found beneath Tilia trees and that Tilia tormentosa is primarily foraged on by bumble bees.
Why this is the case is not clear. However, it is notable that flowers may be attractive to some bee species, yet are ignored by others.
For example, whilst bumble bees will visit borage flowers, they have been found to be more attractive to honey bees, whilst Lavender is more frequently visited by bumble bees9,10.
1. Lande C, Rao S, Morré JT, Galindo G, Kirby J, Reardon PN, et al. (2019) Linden (Tilia cordata) associated bumble bee mortality: Metabolomic analysis of nectar and bee muscle. PLoS ONE 14(7): e0218406. https://doi.org/10.1371/journal.pone.0218406
2. Koch H, Stevenson PC. Do linden trees kill bees? Reviewing the causes of bee deaths on silver linden (Tilia tomentosa). Biol Lett. 2017;13.
3.Pyke GH. Optimal foraging in bumblebees: rule of movement between flowers within inflorescences. Anim Behav. 1979;27: 1167–1181.
4. Owen EL, Bale JS, Hayward SAL (2013) Can winter-active bumblebees survive the cold? Assessing the cold tolerance of Bombus terrestris audax and the effects of pollen feeding. PLoS ONE 8(11): e80061
5. Tilia cordata Small Leaved Lime, Littleleaf linden PFAF Plant Database.
6. Arianna Allio, Chiara Calorio, Claudio Franchino, Daniela Gavello, Emilio Carbone, Andrea Marcantoni, Bud extracts from Tilia tomentosa Moench inhibit hippocampal neuronal firing through GABAA and benzodiazepine receptors activation, Journal of Ethnopharmacology, Volume 172, 2015, Pages 288-296, https://doi.org/10.1016/j.jep.2015.06.016.
7. H. Viola, C. Wolfman, M.Levi de Stein, C. Wasowski, C. Peña, J.H. Medina, A.C. Paladini, Isolation of pharmacologically active benzodiazepine receptor ligands from Tilia tomentosa (Tiliaceae), Journal of Ethnopharmacology, Volume 44, Issue 1, 1994, Pages 47-53, ISSN 0378-8741,
8. Ražná, K.; Žiarovská, J.; Ivanišová, E.; Urbanová, L.; Harenčár, Ľ.; Kováčik, A.; Kučka, M.; Hrubík, P. Flowers Characteristics of Selected Species of Lime-Tree (Tilia spp.) in Terms of miRNA-Based Markers Activity, Mannose Expression and Biological Compounds Content. Forests 2021, 12, 1748. https://doi.org/10.3390/f12121748
9. Quantifying variation among garden plants in attractiveness to bees and other flower-visiting insects’, Functional Ecology, (October 2013). Functional Ecology is a journal of the British Ecological Society.
10. ‘Longer tongues and swifter handling: why more bumble bees (Bombus spp.) than honey bees (Apis mellifera) forage on lavender (Lavandula spp.)’, Balfour, N. J.; Garbuzov, M.; Ratnieks, F. L.W., in Ecological Entomology (online).