Edit: interestingly, I see a lot of honeybees and some wasps foraging, both on the leaves and flowers of the tilia, but it's only the bumblebees that lie dead on the ground.
Every summer, there are dozens of bumblebees either dead or dying beneath tilia trees (linden/lime/basswood).
Why?
My father once told me (some 20 years ago?) that they die from "overeating". With all due respect to his linden tea (thanks dadπ©·π©΅π€), this sounds like folklore...
There was once a thought that the linden tree had a sap that was toxic to bees. A paper that I found claims that the more likely cause of bee death is actually starvation. The flowers of fhe linden tree have little or no nectar late in their flowering stage, but the presence of small amounts of caffeine may mislead bees into believing they are finding a food source. This paper recommends planting alternate late summer flowering plants nearby.
https://royalsocietypublishing.org/rsbl/article/13/9/20170484/50480/Do-linden-trees-kill-bees-Reviewing-the-causes-of The abstract here has some ideas.
Apparently you can revive the ones that are not dead yet by giving them sugar water (2:1 ratio).
I've never heard of any of this, but I found the answers very interesting! Thanks for asking!
If starvation due to the nectar is the cause, then my next question would be, what is the major pollinator for the trees? Or is what they get from everything good enough that evolution doesn't kick in to make this a dead end feature for the tree. Maybe their blooming cycle is different than others, so they tend to dominate at that time and get enough activity even with the deaths?
The other bees can make it further, closer to home. The fat ass bumblebee just plummets like a rock when he loses ANY percentage of propulsion.
Simple answer could be that tilia are hosting Linden Aphid which in turn attract wasps and ants who eat their excretions, and may attack the bee.
I have no knowledge or expertise whatsoever, but could it simply be that the trees are very popular with the bees? Thus theyβre not dying for any particular reason, but since they visit so frequently, many of them happen to die there as well?
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