Posted on  UTC 2017-09-01 02:01

27.09.2017 – Last supper [updated 02.10.2017]

The observation is a commonplace but still a puzzle: in high summer why are there often so many dead bumblebees to be found under lime trees – in particular the silver lime?

The traditional assumption has been that there was something poisonous for bumblebees in the nectar of the lime. If that is so, we wonder, why would the lime tree produce nectar that is fatally toxic to the insects it is trying desperately to attract?

The silver lime tree

The silver lime tree. The underside of the leaves is light and furry, hence the name. Image: Wendy Cutler /, CC BY 2.0.

A group of researchers* at the University of Greenwich now believes that the problem is that the dead bees have simply starved to death at the site of their last attempt to get food.

Lime trees, and particularly the silver lime, flower in high summer, typically from the beginning of July. By that time the other sources of nectar have run out – most plants are now busy making seeds and fruit. The nectar-eating insect world, including bumblebees, of course, descends on the lime as one of the last sources of nectar for the year. That source is too meagre for its popularity and the bumblebees die of hunger and exhaustion at the site of their hopes of the next meal.

The research team concludes that instead of regarding the lime tree as a bee-killer and suppressing it, we should, in fact, be planting more of them and also the other plants that deliver the last food sources of the summer. The extension of the feeding season would contribute greatly to the survival of bumblebee colonies.

*The paper, in Biology Letters, is paywalled. H/t instead to Neue Zürcher Zeitung [DE].

Update 02.10.2017

Since posting this piece some additional, well-documented information [DE] has come our way:

  • Bumblebees miss out on the hearty breakfast that is so essential to a successful day. Late in the season they set off on a nearly empty tank and when that is empty, that's it – they don't have the energy to get to another source. Some can be rescued with a drop or two of sugar solution, but some are too exhausted to even drink it.
  • This desperate state is starvation, not tiredness: a rest will not help.
  • Bumblebees cannot communicate among themselves about food sources in the way that honeybees do. They tend to keep going to the same source, since with low fuel reserves just flying around in the hope of finding food is not an option.
  • Bumblebees stick with their known source even when a good alternative is close at hand. They seem to die of hunger on the flower they know rather than risk their last drop of energy on the flight to an unknown plant. When the known source runs out they have had it.
  • They seem to be able to copy what other bumblebees do. When they see bumblebees on other flowers they will join in, but otherwise ignore unknown flowers. When flying on empty there is not much time left for learning.
  • These factors mean that it is difficult for bumblebees to keep up with the changes of source during the pollination season, particularly towards its end. When the silver lime tree that has been feeding them for a few weeks dries up, they lack the flexibility and the spare fuel to buzz off and look for some other source.

26.09.2017 – A century of progress

William Briggs, 'Statistician to the Stars!', himself a snappy dresser, had an amusing image heading a post on the decline of civilisations that just said 'steal me!' to us.

Image from William M. Briggs : Statistician to the Stars!

Left: Cary Grant (1904-1986), thirteen years old in 1917…

24.09.2017 – Please, Lord, let they handmaid depart in peace (ASAP).

The top item on Theresa May's shopping list is the regulation of 'the internet'. Content platforms of all kinds will be threatened with huge fines if terrorist material is displayed for longer than an hour or two. The idea is technically and politically a non-starter, but the fact that she could not only think it but she was even prepared to waste most of her speech to the General Assembly of the UN on this shopping list item only illustrates how dim she is. Or how malignly authoritarian she is. Or both? Yes, both.

For 'terrorist material' read 'whatever the Government does not like' and for that read 'whatever content platforms think some government might not like'. A large range of such material will be taken down, just in case. Within a short time, even we harmless bumblers on this website would be unpublishable.

Do the great minds of Government not realise how such a regulation, if they ever managed to bring it into effect, would stifle public debate? Yes, they probably do.

24.09.2017 – Keeping an eye on the Germans

German Federal Election today. The electoral spoon will stir the alphabet soup and bring up some different letter combinations, but it is all the same. Nothing will change. Having learned the lessons of history the hard way the German constitution has created a political pyramid that cannot be pushed over.

The worst that can ever happen is a grand coalition between the CDU/CSU and the SPD, which is almost a definition of the status quo. The prospects of the AfD are being talked up, just as in previous state elections, but neither of the two big blocks will enter a coalition with them. So it looks like Merkel and Schulz, one alone or both together. Nothing will change. Torchlight procession, anyone?

23.09.2017 – The school run – alpine style

The children from the farms up on the hillside have to park their bikes some way from the school.

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There's a gorge in the way.

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There are still some places in the world where bikes don't have to be chained up and health and safety is a matter of common sense, not requiring warning signs.

23.09.2017 – How to become a published author

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