The gentle buzzing of bumblebees is one of the iconic sounds of the British summer. But how will our favourite furry bees respond to the UK’s unprecedented temperatures?

Bumblebees are built for cooler climes. Unlike most insect groups, they actually prefer the milder temperatures of the temperate regions – that’s why Britain has almost 10% of the world’s bumblebee species, a much higher proportion than for most other insects. The reasons for this date back around 35 million years, to the proto-bumblebees of northern India.

At that point the Himalayas were a relatively low mountain range, with some fairly average bees. But as the Indian sub-continent pushed into Asia, the climate changed to become cooler and damper, and the bees had to adapt to survive. They already generated a lot of heat through flapping their wing muscles, but they became furrier, to keep that heat in, and rounder and larger to reduce surface area to stay warmer for longer. Eventually they became our familiar bumblebees.

But their adaptations limited their options. They were so good at remaining warm, that if they tried to fly in hot climates they couldn’t vent heat quickly enough. In trials, the American Yellow-faced bumblebee Bombus vosnesenskii started to overheat after just three minutes of flight at 42°C. The bees started trying to cool their heads by regurgitating a droplet of nectar and stirring it round with their proboscis, increasing the surface area and cooling their heads down by around 2°C. When temperatures reached around 44-45°C, the bees did this even without flying.

That temperature intolerance meant that instead of dispersing south from the Himalayas into the tropics of Northern India, they had to spread northwards, into the cooler temperate regions of Asia, Europe and North America. It’s also the reason why, in the tropics, bumblebees are generally found at high altitudes, where it’s that bit cooler.

Britain, then, was more or less ideal for the group with our mild summers. Our general lack of drought suited them too – warm and wet is good plant-growing weather, which means lots of pollen and nectar available all summer. We know that drought stresses plants, causing them to produce fewer flowers, smaller flowers, and less nectar and pollen within flowers, and that droughted flowers attract fewer bees. Hot, dry landscapes are worse for bees than warm, damp areas.

British bumblebees aren’t as temperature-tolerant as Bombus vosnesenskii.  In the UK, bumblebee activity starts to drop off at around 28°C. Cuckoos and males tend to tuck themselves away in the shade and wait it out: workers keep foraging, but species gradually give up as they reach their thresholds. Buff-tailed and Red-tailed seem to be the last to go, along with some of the rarer southern species. Once temperatures reach about 32°C, virtually all outside activity ceases, though nest-fanning (workers using their wings to blow air through the nest) will continue.

Bumblebees are still able to forage on hot days – they’re out first thing in the morning and last thing at night, they just need more of a siesta in the middle of the day. But that cuts into their foraging time, and drought-hit plants are less rewarding to visit – the day’s foraging suddenly brings in a lot less food for the colony. For bumblebees that are already struggling, that isn’t great news.

Dr Richard Comont, Science Manager

Twitter @RichardComont

With the world talking climate, our science team take a look at what a changing world means for the UK bumblebees.

6 December 2021

By Dr Richard Comont, Science Manager and Darryl Cox, Senior Science and Policy Officer

With the world talking climate following COP26, our science team take a look at what a changing world means for the UK bumblebees.

At a global scale, bumblebees are cool-weather creatures, most at home in the world’s cool, damp temperate regions. The climate of these areas is predicted to be changed substantially by global warming.  Research on bumblebees’ global ranges finds that, as the climate warms, the area of hospitable conditions for each species (its climate niche) is moving towards the Poles. Therefore, bumblebees in Europe will need to move northwards to stay within their niche.  This will be particularly apparent at the southern edge of species’ ranges: if species don’t manage to move northwards fast enough, they won’t survive.

Most of our UK species are towards or at the northern edge of their ranges in Britain.  These species may become more widespread across the country in the near future – for instance, the northwards movement of several species such as the Buff-tailed bumblebee (Bombus terrestris) over the past few decades is likely to be at least partially linked to the changing climate. However, we also have species which are close to their southern range edge. These species are likely to be more and more at risk as the climate changes, and the size of their habitable areas shrinks. For example, the Great Yellow bumblebee (Bombus distinguendus) is now only found on some Scottish islands and a thin strip of the mainland north coast, and the Moss carder bee (Bombus muscorum) is widespread in Scotland but undergoing a severe decline further south, in England and Wales.

Other species are at risk because they are specialised to a habitat which itself will decline as the climate warms. The Bilberry bumblebee (Bombus monticola) thrives on bilberry moorland, mostly above 300m. As climate change takes effect, the habitable zone for these species moves not just northwards but also uphill, leaving smaller areas of isolated habitat (essentially, hilltops) which eventually become too small and the species will die out there.

For bumblebees to survive in a climate change world, they must be able to move northwards, tracking their habitable zones. There is evidence that species’ southern range edges are moving northwards, and other species are moving uphill. Concerningly, however, there is little evidence of northwards range shifts, meaning species ranges are growing increasingly restricted. A recent climate risk atlas for European bumblebee species found that most species are likely to decline significantly under current warming scenarios.

So why should this be the case? Well, we know that bumblebees also experience other pressures and, in the UK and across most of Western Europe, the historical driving force behind bumblebee declines has been the loss and fragmentation of bumblebee habitat, driven by development and the intensification of agriculture. In fragmented and flower-depleted landscapes, it is more difficult for species to move through the landscape and migrate into new areas. This is particularly difficult for species which are more sensitive to habitat quality, for example those with stronger preferences for particular flowers or shorter foraging ranges, and for those species which are not strong dispersers. In both cases the nearest suitable habitat is likely to be too far away or too hard to reach. The combined effect of climate change and habitat loss & degradation is to leave small pockets of populations isolated in areas which are becoming increasingly unsuitable for them – like fish in evaporating puddles after a flood.

Of course, climate change doesn’t just mean that temperatures increase: it also increases the frequency and severity of extreme weather events like floods, storms and droughts. It is these which will present the most immediate climate-related impacts for bumblebees in Britain.  Floods can wipe out hibernating queens, and colonies nesting in the ground. Severe droughts can reduce nectar availability at critical points of the colony lifecycle, reducing the nest’s production of new queens – next year’s colonies. Increased storm frequency and severity, particularly allied to sea level rises in coastal areas, could have severe impacts for some of our rarest species. Many of these are now largely coastal, or are restricted to low-lying areas such as the Somerset or Gwent Levels at risk of seawater infiltration or flooding.  The Great Yellow bumblebee, one of our rarest species, is almost entirely restricted to the machair, dune grasslands at risk from Atlantic storms and rising sea levels.

More widely, shifts in seasonal patterns such as earlier springs could create a mis-match of timings between flower availability and bumblebee queens. Queen bumblebees emerging from their winter dormancy need to find nectar as soon as they can in order to recover from their long months of hibernation. Queens then need to find both nectar and pollen as they establish a nest on their own. Reducing the food available to them at this crucial point can have a major effect on survival.

What can be done to help bumblebees combat climate change? 

Obviously a key thing is minimising the amount of climate change that happens. Without this crucial step, other actions are treating the symptoms rather than the root cause.

Unfortunately, even in the best-case scenario there will be a considerable change to the climate and we must help bumblebees to survive the change. We know that well-fed bumblebees with high-quality places to nest and hibernate are better able to respond to the challenges they face. The priority for bumblebees therefore remains getting flowers back into the landscape and ensuring they have flowers available right through their flight season, March-October. This is something that everyone can help with, from individual gardens or window boxes, to community greenspace planting, right through to large-scale meadow creation. Our Bee the Change campaign has resources to help you achieve this.

Thankfully, meadow creation – one of the very best ways to help bumblebees and lots of other wonderful wildlife – is also a really good way of storing carbon in our landscapes. By restoring or creating the flower-rich grasslands we have lost over the last hundred years, we can help our plant life and wildlife to recover and tackle the climate crisis. Increasing the abundance and diversity of flowers in these habitats boosts biodiversity and increases the amount of carbon stored in the soil below. Take a look at our Land Management for guidance.

Beyond providing food and habitats for bumblebees, you can join in with the Bumblebee Conservation Trust’s work through attending an event, volunteering, donating, or becoming a member to help create a world in which bumblebees can thrive.

Kirk Mason joined the Trust as a volunteer in November 2020, after attending our session at the University of Derby online volunteers fair, where he is currently studying, in the October. Kirk explains why he wanted to help and how he is currently doing this . . .

As an aspiring entomologist, it’s the time of the year where I always get itchy feet. Soon, it will be time to find bumblebees and other amazing insects – Spring is drawing close! Though each year, chance encounters with some of these amazing animals feels increasingly rarer.

Through my Zoology degree, it became apparent that pollinators such as bumblebees are incredibly important to the wider landscape. The service they provide, supports life from the ground up, by helping many flowering plants reproduce. These plants provide food for lots of animals such as insects, birds and mammals – including us! When I learned that more than a third of bumblebee species have declined by 70% in Britain between 1900 and 1980, I was shocked. Shocked that creatures, so charismatic, industrious and important could cease to exist in the future because of our activities – not through ill intentions, but simply not knowing.

This led me to read into how we can reverse these declines and prevent bumblebee extinctions. It quickly became apparent that the Bumblebee Conservation Trust are leading the fight to conserve bumblebees in Britain. How? Through conservation projects, education, helping land managers, research and engaging with people. The Trust also trains members of the public to contribute to citizen science projects (BeeWalk), which are incredibly important in developing a greater understanding of the bigger picture in Britain. After learning this is what the Trust does, I thought “I want to be a part of that!”

So, how am I contributing? For now, I’m helping with public engagement online, by contributing to the Trust’s social media through writing and photography. When I started volunteering with the Trust, I immediately felt at home due to the community spirit amongst the staff and volunteers. The positive and supportive mentality of everyone involved makes for an excellent collaborative environment, where everybody shares a common goal – to conserve our bumblebees.

Once restrictions lift, I hope to help with face-to-face engagement and physical activities such as habitat management. Though there are many ways that we can help, some of which I hope to try! There are green-fingered activities such as bulb planting, growing seeds and cuttings. Surveying through walking outdoors, looking for bumblebees and documenting results is a crucial way of contributing to our scientific understanding of bumblebees. Talks, guided walks and fundraising are great ways of talking about bumblebees with people and helping at the same time. There are admin duties, preparing event resources and even data handling opportunities. Becoming a member of the Trust really helps and no matter your skill set, there are many ways to contribute in the fight to conserve British bumblebees!

See how you can get involved by visiting out volunteering page here. 

13 November 2020

Ten years ago On the Verge founder, Leigh Biagi, was in her kitchen making packed lunches, when she heard Professor Dave Goulson, founder of the Bumblebee Conservation Trust, talking on the radio about declining bee numbers. On the Verge is a Stirling based, voluntary, community project established in 2010. This is her story…

I had just started studying for a degree in Environmental Studies with The Open University and was feeling a bit desperate about the state of the planet, so when I heard Dave say that several species of bumblebee had already gone extinct, and others were on the verge of extinction it really resonated with me. I thought ‘On the Verge’ would make a great name for a bee project and somebody should really set one up. I couldn’t stop thinking about it and by the end of the day, I had decided to do just that.

I explained my idea to a friend who worked in the environmental sector; she helped to gather together a group of like-minded people and ‘On the Verge’ was born!

Dave Goulson had explained in his radio interview that pollinators were beginning to gravitate towards towns and cities, as urban environments offered better food sources thanks to the British love of gardening. We decided that if bees were clever enough to adapt, then we should be clever enough to help them by providing as many areas of native wildflowers as possible.

So, we initially decided to approach schools and community councils to achieve a good geographic spread of wildflower sites throughout the city.

I was worried that nobody would be interested in the early stages, but it soon became clear that plenty of people were keen to get involved, particularly schools, and then I worried too many people would be interested and we wouldn’t be able to cope and there was certainly plenty for us to do in the first year.

The first issue that needed solving was funding. We approached ten local businesses who each donated £100 to get the project off the ground which was wonderful.

The next question to tackle was what the best seed mix to sow was. We worked closely with Scottish wildflower seed producer Scotia Seeds and a special ‘On The Verge’ wildflower mix was developed, comprising four annual species and eighteen perennial species, all native to the UK.

The final hurdle was finding someone to prepare the sites. Luckily, somebody directed us towards Stirling’s Criminal Justice Service, and they agreed to prepare the On the Verge sites for sowing.

I then decided to approach Stirling council to ask them to sow some wildflowers as well. I just wanted them to sow a couple of small, high-profile areas in support of the project. I was amazed when they agreed to establish 25 sites throughout Stirling in the first year, totalling 1,440 square metres.

That was ten years ago now, and since then we have sown a total of 10,000 square metres of native wildflowers in partnership with over 90 local organisations including 26 schools,7 nurseries, 2 care homes, 3 churches and 4 scout/guide troupes.

We are an entirely voluntary organisation and we work in three key areas; providing free seed, practical support and advice to community groups to help them sow areas of wildflowers; attending community events and giving talks to promote the work; and collating data for research projects with students from Stirling University.

We also work with community groups to improve existing wildflower meadows using seed which a few of us collect locally, and have plans to introduce ‘Bee Beds’, using nectar-rich, perennial planting as a neater alternative to wildflower patches.

Project highlights include; a Nature of Scotland award from the RSPB in the species champion section in 2011; jointly  hosting the 2015 Inspiring Meadows conference with Stirling Council, Buglife and Inner Forth Landscape Initiative; being chosen as one of the projects highlighted by Chris Packham in his 2018 UK Bioblitz campaign; and in 2020 featuring as a case study in the Wildlife Trusts Reversing the decline of Insects.

We are also branching out; in 2019 we were joined by our sister group On the Verge Cambridge and we are currently working to help set up an ‘On the Verge Perth’.

2020 has brought about some changes for On the Verge. Due to COVID-19 restrictions, we weren’t able to sow with any of the schools as planned, which was a pity, but it did give more time for thinking and planning. This year grass-cutting in Stirling was delayed until June and walking around the city’s greenspaces this spring I saw wildflowers that I’ve never here seen before, because they are usually cut down before they have a chance to flower. It occurred to me that it was a bit ironic for ‘On the Verge’ to be sowing new areas of wildflowers at the same time as the council was mowing out the existing wildflowers in the grassland.

I decided to launch an online petition asking Stirling council to take a more ecological approach to manging local grassland in order to help local insect populations, particularly pollinators.

One of the most important things the petition asked the council to do was to adopt a cut and collect method of grass management. Currently when grassland is mowed the clippings are left in situ to rot down. This releases nitrogen which fertilises the grass and so it grows back vigorously and out competes the wildflowers. If the clippings are regularly lifted off-site, then over a few seasons the grass weakens allowing the wildflowers to flourish resulting in less grass, more flowers, and healthier pollinators, all because of one small change.

The petition received over 1,500 signatures and was presented at a council meeting on the 24th September where council members agreed to proceed with the recommendations made which was a fantastic response.

We have now begun to work with groups from all over the country, helping them to lobby their own local authorities for change, including groups from Cambridge, Worcester, and Perth. We are very keen to hear from more people who might be interested in improving their local areas in this way. The hope is that by working together we can persuade many other local authorities to follow Stirling council’s lead and by working collectively, we can do a great deal to protect the UK’s natural environment.

On the Verge can be contacted at enquiries@ontheverge.co.uk / Facebook  / Website

Twitter @OTVStirling