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Bumblebees and climate change

Posted: Wednesday 13 March 2013
by Richard Jones

Sapphire Class at Ivydale Primary School are now experts on bumblebees. We did a workshop on climate change so I took in a tray of bumblebee specimens.


Bumblebee

Sapphire Class at Ivydale Primary School are now experts on bumblebees. We did a workshop on climate change so I took in a tray of bumblebee specimens and we talked about the potential consequences for these well-known and much-loved insects.

First we looked at a few basic aspects of bumblebee biology; the nine and 10 year olds knew quite a bit already, but learned (I hope) a lot more.

  • They knew that bumblebees sting, they didn’t know it was only the females — the stinger is a modified part of the egg-laying equipment, so the male doesn’t have one, obviously.

  • They knew bumblebees are furry, they didn’t know that this insulates them against the cold so they can forage earlier in the year than other insects, and earlier in the day, and further north, and further up mountainsides.

  • They knew that bumblebees visit flowers to collect pollen and nectar, but they didn’t know that despite pictures on the side of many a jar, we do not get honey from bumblebees, that’s honeybees. I’m quite a stickler for this simple fact, and I was very quick to put them straight on it. [Technically, bumblebees do make an extremely small store (a few millilitres) of thin nectar regurgitation, but this is nothing like the huge stocks of thick, sterile, sweet gloop stored against winter and hard times in the honeybees’ wax comb, and which gives a honeybee colony virtual immortality.]

The pupils also knew a lot about climate change — ocean acidification, changes in ocean salinity, water level changes, ice sheet retreat, carbon dioxide emission, and fossil fuels. We were concentrating on global warming, just one of the aspects of climate change I know, but one that most people can understand easily. What does this mean to bumblebees?

What it might mean is that as global temperatures rise, cool-adapted organisms like our furry bumbles, would become harder and harder pressed in the southern lowlands, from which they are already retreating in the face of industrial agriculture.

To keep to a habitat for which evolution has adapted them over many millions of years, they may have to migrate north to keep to the relatively narrow belt of climate, temperature, humidity and season length, which they find comfortable. A rough estimate is that they will need to move about 200 km north to deflect each 1ºC increase in average yearly temperature. Likewise, those boreo-alpine species will have to move about 100 metres further up a mountain, for each degree, to keep within their favoured temperature range.

At first, this may not seem such a great inconvenience, bumblebees are relatively mobile. Northward colonisation has recently taken place in the tree bumblebee, Bombus hypnorum, which arrived in Britain in 2001, and has now just about reached Scotland. But many of the scarcer species are already limited to far northerly localities and some are specialist montane rarities. It does not take many degrees temperature increase before these already high-altitude bees are at the top of a mountain, and have nowhere else to go, except into extinction.

Likewise, it is not far (especially in the UK) before some of the northern specialists run out of land and are faced with only the rough waves of cold northern seas. This is a scenario to be repeated across the entire northern hemisphere. Even if we don’t get total extinction, we are likely to suffer biodiversity loss.

Anyway, back to gardens. I had hoped to bring a live bumblebee into class. The very day before I had seen a huge buff-tailed (Bombus terrestris) queen sniffing out the daffodils growing in flowerpots outside the school office. But the day of our lesson was wet and grey, and it has remained pretty damp and cold ever since. No bees are flying now.

Although it is a more difficult concept to grapple with, it is the subtle local weather changes around the edge of global warming that are, perhaps, a more insidious threat. Bumblebees are well-adapted to cool climates, and they can happily overwinter under feet of snow, but the limiting factor on their spring foraging, during the all-important period of new nest foundation, is unpredictable wet and damp. The queens, still working alone before they have reared their first generation of workers, cannot get out to feed, or collect nectar and pollen for their brood, the subterranean nests are liable to flooding, and nest, brood and roosting queens are all vulnerable to mould and fungal disease.

The most important thing we, as gardeners, can do to help bumblebees at this time of year is not to fuss too much about nectar plants, but to make sure we provide plenty of grass tussocks, log piles, rough corners, and untidy edges where the bees can find safe dry shelter, for roosting and nesting, whilst they are waiting for spring to really come along.

Bumblebee specimens




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