Bumblebees active in winter in the UK

These include the very common 'Buff-tailed Bumblebee' (Bombus terrestris ssp. audax). Queens of this sub-species tend to be large and wide, with a pale peachy-buff coloured tail. Workers have a white tail. Sub-species audax is confined to Britain and Ireland. If you cross the Channel you will find that in Northern France B. terrestris queens have a white tail.

Foraging from Winter-flowering garden plants

Evidence to date
Recent evidence suggests that in some areas of the UK the Buff-tailed Bumblebee is producing winter colonies in addition to its summer breeding cycle. It relies on autumn and winter-flowering plants growing in gardens as a forage source. Prime amongst these are Arbutus, and Clematis cirrhosa, from the Mediterranean area; Mahonia and winter-flowering honeysuckles such as Lonicera fragrantissima, from Eastern Asia; and Erica carnea, a winter-flowering heather from the European Alps. There are very few native British plants that flower in the winter, and it seems that those that do (e.g. Gorse) do not provide sufficient or suitable forage to support winter bumblebee colonies. For this reason it is unlikely that winter colonies will survive in the open countryside away from gardens.

Favourite flowers of bumblebees in autumn and winter:

Left:
Arbutus



Right:
Lonicera
fragrant-
issima

.

Left:
Erica carnea
with
B. terrestris

Right:
Mahonia

.

Interestingly, there are many conspicuous winter-flowering plants that the bees do not seem to use as a regular forage source, or only visit as a last resort. These include Viburnum x bodnantense, Chimonanthus praecox, Jasminum nudicaule, Cornus mas, Iris unguicularis, and winter bedding plants such as pansies and polyanthus. The fact that they do not seem to visit these may be because these plants do not produce suitable nectar or pollen, or possibly it is inaccessible to the bees.

Ecology of winter bumblebees

Bombus terrestris in Southern Europe
The winter nesting behaviour of the Buff-tailed Bumblebee in the UK may not be as aberrant as it first seemed. Bombus terrestris in a broad sense is widely distributed in Europe, and a number of sub-species have been recognised. In the Mediterranean area, the local sub-species exhibit regular autumn and winter breeding behaviour, which fits in the with the local climate and the availability of forage plants such as Arbutus unedo, A. andrachne and other autumn and winter-flowering species.

Is this a reaction to Climate Change?
Many kinds of insects in the UK have expanded their distribution northwards in the last 20 years, and it is generally thought that this is due to the milder winters we now experience. The winter breeding behaviour of the Buff-tailed Bumblebee is particularly interesting because it appears to be a change in behaviour, rather than a change in distribution. It is still hard to go beyond this and make firm statements about this phenomenon without the collection of much more data, over a wide area, over a number of years.

Should we all plant more winter flowering shrubs as food for bumblebees?
Not necessarily. B. terrestris is very common and is not a species of conservation concern in the UK at present. In fact if it can successfully breed in winter in the UK it might gain a competitive advantage over some of the other common Bumblebee species, for example by monopolising potential nest sites early in the year, so that the other species might suffer. As yet we just don't know - we need more data, from more sites, collected over a number of years. This is where you can help.

Did you see winter bumblebees in your area?

This is your chance to get involved. Of particular significance is the recording of males, as this is evidence that a winter colony has been successful - males tend to be produced towards the end of the life of a colony. Evidence of colonies in the open countryside, away from gardens, would also be interesting. A few winter records of another species, Bombus pratorum have been received by BWARS. More winter records of this species would be particularly interesting, because as yet there is sparse evidence of other species apart from B. terrestris showing winter nesting behaviour. The photo on the left shows a typical B. terrestris queen with her buff-coloured tail.

Here's how you can help to fill the knowledge gap:

• You should submit your winter bumblebee records to BWARS. Their winter bumblebee page has a distribution map and a downloadable information sheet.

• Summer records of bumblebees are also required on a large scale so that we can get a picture of their distribution and relative abundance and how these change over time. The Bumblebee Conservation Trust (BBCT) runs various surveys.

• If you participate in the British Trust for Ornithology's Garden Birdwatch, there is a supplementary bumblebee monitoring sheet you can also fill out.

The Big Freeze early in 2010

I wrote the text above and posted it on this site in December 2009. A couple of weeks later the big freeze started that has led to one of the coldest and snowiest winters for many years. It is very unlikely that the Autumn 2009 crop of B. terrestris colonies that were foraging in December 2009 will survive. There is even concern that the very low temperatures experienced in the north of the UK will freeze normally hibernating queens of all bumblebee species.

This is all the more reason for us gardeners to get interested in systematic Bumblebee recording and bumblebee conservation. Only by comparing large numbers of Summer 2010 bumblebee records from around the UK with those for previous years will we be able to ascertain whether numbers have fallen. The more information we can gather about the reactions of bumblebee populations around the country to our unpredictable weather, the more that can be done to conserve them.

How I got involved
I originally became interested in this subject in 2005, when I noticed bumblebee workers (non-reproductive females that forage for nectar and pollen) visiting an Arbutus (Strawberry Tree) in my garden in November and December. According to the books then available this was not possible, because bumblebee colonies die out in late summer and only individual young queens (fertile females) survive the winter in hibernation to found new colonies the following spring. The presence of worker bees on a regular basis suggested that there was an active nest nearby. I wrote an on-line article on this subject for the 'Space for Nature' wildlife gardening website. That website is no longer being developed, but at present it remains available as an archive and you can view my 2005 article here.

At that time I was studying Ecology and Conservation as a part-time student at Birkbeck College, University of London. I had to choose a dissertation subject and I decided to investigate the phenomenon of winter bumblebees. I collected data by regularly walking a 1km fixed route (transect) in the area of suburban London where I lived at the time, to record any observations of winter bumblebee activity in 2006/7. The exercise produced a lot of data.

I repeated the exercise the next winter, 2007/8. I was able to arrange a transect in Kew Gardens, which passed many winter-flowering plants. Again, this produced a lot of data.

Detailed research into the mechanisms behind, and consequences of, the winter generation in B. terrestris is currently being undertaken by Dr Tom Ings from Queen Mary, University of London, who is also continuing the survey work at Kew Gardens.
Tom's website is at http://webspace.qmul.ac.uk/tcings/