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.

9 March 2020

The Trust has published a new position statement on managed honeybees. The statement has been prompted by concerns that, under certain circumstances, managed honeybees can have detrimental impacts on wild pollinator species, including bumblebees.

Our Senior Science & Policy Officer, Darryl Cox, provides the background on why we’ve decided to publish the statement.

Q1. What prompted the Trust to produce the position statement?

There is an increasing body of research which shows that, in some situations, beekeeping can have negative consequences for bumblebees (and potentially other pollinators) by increasing competition for food and by passing on diseases. These negative consequences are most marked in areas where there are fewer flowers or higher densities of honeybee hives, and could potentially be serious where vulnerable populations of wild bees are present. This statement aims to mobilise that research into action and highlights important steps that can be taken by beekeepers, conservationists, and anyone else with an interest in helping bumblebees, to lessen any potential negative impacts of managed honeybees.

Q2. Is all beekeeping bad for wild bees?

No. The message is not that beekeeping is bad, and it’s definitely not something we want to avoid or prevent. Our aim with this statement is to help inform people of best practice and encourage responsible beekeeping and well-thought-out hive placement. Keeping honeybees is important economically for honey and wax production, and for pollination of some crops and wild plants, as well as being firmly embedded in our culture. Several of the Trust’s staff and supporters are beekeepers, and are also some of the biggest advocates for wild bee conservation. The important bit is finding the middle ground that balances wild bee conservation and beekeeping, and making sure that rare wild bees aren’t inadvertently harmed.

Q3. What are the main recommendations?

The main recommendation is to take a precautionary approach to how we do beekeeping so that we do not accidentally end up causing problems for our wild pollinator communities. Five specific recommendations are made in the statement which outline how the precautionary principle can be applied in practice.

The position statement is available here.