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 dad🩷🩵🤍), 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.
small amounts of caffeine…believing they are finding a food source
Huh, I’m more similar to bumblebees than I thought!
First day off the coffee, and sitting around confused and hungry, and now this bit of information. Well I guess I need to feed myself with real food now. Okay.
Thank you for this link.
https://royalsocietypublishing.org/rsbl/article/13/9/20170484/50480/Do-linden-trees-kill-bees-Reviewing-the-causes-of The abstract here has some ideas.
Abstract
For decades, linden trees (basswoods or lime trees), and particularly silver linden (Tilia tomentosa), have been linked to mass bee deaths. This phenomenon is often attributed to the purported occurrence of the carbohydrate mannose, which is toxic to bees, in Tilia nectar. In this review, however, we conclude that from existing literature there is no experimental evidence for toxicity to bees in linden nectar. Bee deaths on Tilia probably result from starvation, owing to insufficient nectar resources late in the tree’s flowering period. We recommend ensuring sufficient alternative food sources in cities during late summer to reduce bee deaths on silver linden. Silver linden metabolites such as floral volatiles, pollen chemistry and nectar secondary compounds remain underexplored, particularly their toxic or behavioural effects on bees. Some evidence for the presence of caffeine in linden nectar may mean that linden trees can chemically deceive foraging bees to make sub-optimal foraging decisions, in some cases leading to their starvation
caffeine
OK so, superexcited bees become too stupid to make rational decisions. Relatable.
Well I’ll be damned
Apparently you can revive the ones that are not dead yet by giving them sugar water (2:1 ratio).
It’s basically a redbull to them. They get a big energy surge and can do stuff again. With a bit kf luck, they get enough energy to fly home and recover there.
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.
I have no knowledge or expertise whatsoever, but could it simply be that the trees are very popular with the bees? Thus they’re not dying for any particular reason, but since they visit so frequently, many of them happen to die there as well?
Ah, a connessuier of aeroplane chickenpox!
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.
Are these the guys who make it occasionally feel like it’s raining under the Linden?! Gross and fascinating 😱
