Whilst some lime trees are toxic for bees, others provide a very useful nectar source. Reputedly some lime trees (tilia) are poisonous for some bee species and less toxic for others, or have at least a narcotic effect. Such an effect will obvioulsy make the bees vulnerable to 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 a case I personally heard about.
Dead bumblebees had been found beneath a lime tree with parts of the abdomen missing. It transpired that Great tits had taken advantage of bumblebees feeding on a lime tree, and had eaten the parts of the bumblebee they apparently find most appetizing!
Some lime trees (also known as Linden trees) are favoured by beekeepers, and Linden honey is especially popular in Romania, for example, but Linden does not produce propolis. Bees may also harvest the honeydew produced by aphids on the leaves.
Generally, it is thought that non-toxic limes are:
The following lime trees are regarded as poisonous for bees (or having an unfortunate/narcotic effect or hamper the bee in some way), and so should be kept out of the bee garden:
Lime trees are said to have a short flowering season. My advice would be, that if you are considering buying lime trees to include in a bee garden, perhaps consider different species of trees instead – take a look at these trees, shrubs and hedgerows for bees.
On the other hand, if you are keen to include the lime in your garden, consider Tilia platyphyllos or tilia cordata, since it is generally considered that both of these species of lime trees are safe for foraging bees.
This is as yet unclear, but having read a number of research papers, any notion that some bumblebees simply starve themselves to death by drinking so much lime tree nectar that they run out of energy and die before returning back to the nest, lacks credibility in my view.
This seems highly unlikely to me because if the bees keep feeding, surely, they are obtaining energy from the nectar they have just been feeding on, and so how can they have 'run out'. Why don't they 'run out of energy' after feeding at other highly melliferous plants, such as borage and comfrey?
It also fails to explain a number of other results I have read from research.
My own (untested) theory is based on the theory of the founder of toxicoloy, Paracelsus, which is:
"The dose makes the poison"
"All things are poison and nothing is without poison; only the dose makes a thing not a poison."
Thus my theory is that in the same way that clean water is healthy and necessary, but even water could kill you if you drink too much in one go, then I wonder if the same is true for some bees and lime trees - i.e. sometimes the bumblebees enjoy the nectar so much, they consume too much of it, such that it has a narcotic or even poisonous effect.
Why this should be the case sometimes for bumblebees and not honey bees is also unclear, but I wonder whether this is connected with the strength of the 'homing instinct'. We already know that a bumblebee may fly upto 1.7km for food, whereas honeybees are known to fly upto 20km. Does this suggest that in the case of honeybees, the natural instinct to return to the colony is stronger, enabling a successful return from longer distances?
I don't know, but since nobody has any definite answers yet, it's interesting to guess!
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