Catherine Zentile

The Plight of the Bumblebee

Why Britain's losing it's buzz...

The unmistakeable buzz of a bumblebee is one of the quintessential sounds of British summertime. But this ‘slender sound’ and ‘faint utterance’ that was so admired by Wordsworth is under threat, because bumblebees are in crisis. Of the 25 species native to Britain, three have already been declared extinct (the latest casualty being Bombus subterraneus in 1988), five are designated UK Biodiversity Action Plan (UKBAP) priority species, and many more have undergone major range contractions. The great yellow bumblebee, Bombus distinguendus, for example, is now restricted to northern Scotland, Orkney and the Hebrides, and the shrill carder bee, Bombus sylvarum, which was once common throughout southern Britain, now exists only in seven small groups. And as these populations become more isolated they can become inbred, which increases the risk of further extinctions.

Background to bees

At the end of summer all the bumblebees in a colony die, apart from the virgin queens who mate and then leave the nest to hibernate over winter. In the spring a queen will make a new nest, lay eggs and then raise the first batch of workers. This annual cycle depends on there being enough pollen and nectar to sustain the queen as she establishes her nest and team of workers as the colony grows. Pollen is a protein-rich fuel that is key to helping over-wintered queens to kickstart their reproductive systems ready and for the development of larvae. Nectar, on the other hand, is a sugar-rich fuel which is converted to honey to feed adult bees. The bees make honey by adding to the nectar in their honey sacs an enzyme called invertase, which converts sucrose sugars to a mixture of glucose and fructose. Once the workers are developed, they take over the foraging and the queen concentrates on laying eggs. Later in the year, if the colony has been successful and reaches a large enough size, the queen will produce male eggs and some female eggs are raised as new queens.

Under threat

But why are bees in decline? A lack of resources is thought to be the critical factor that's affecting bumblebee populations and it's related to the loss of wild flowers, both in the countryside and in vast areas of suburban gardens. "We think the biggest impact has been the availability of food and drink, in particular the continuity of supplies throughout the colony cycle" say bumblebee experts Lucie Southern and Robert Dawson from the Bumblebee Conservation Trust, BBCT. "Although nectar is available from a wide range of plants, the bees can be much more choosy about where they collect pollen from, sometimes restricting this to very few flowering plants."

In Scotland, overwintered queens of the declining and beautiful blaeberry bumblebee (left) focus on bilberry (called ‘blaeberry’ in Scotland) in spring. Other species may focus on legumes such as red clover and bird’s-foot trefoil. Sadly, because the UK has lost 98% of its flower-rich grasslands, this has been devastating for some bumblebee species.

Does the plight of the bumblebee matter?

Bumblebees, like honeybees and many solitary bees, are crucially important pollinators. No detailed study has been completed for bumblebees but it is known that their honeybee relatives have an estimated value to the economy, in terms of pollination alone, running into hundreds of millions of pounds. Since bumblebees are more widespread and more abundant than honeybees they probably account for a similar amount. "Bumblebees are ‘buzz’ pollinators: they generate a high-pitched buzzing frequency which causes the release of pollen, allowing them to pollinate plants such as tomatoes. In Australia, where there are no bumblebees, people have to do this by hand," explains Southern. So farmers growing crops like broad beans, runner beans and raspberries depend on bumblebees to achieve a reasonable yield.

Can we combat the bumblebee decline?

Thankfully all is not lost because there are some simple steps that we can all take to make bees' lives easier. Top of the list is to plant bumblebee-friendly flowers and shrubs in the garden: a pot of herbs such as sage, rosemary, lavender and chives can be great for bumblebees.

But don't be fooled by flowers because, unfortunately, modern bedding plants that have been bred to produce dazzling displays usually have little in the way of pollen or nectar, and what little they do have is often inaccessible to the insects, which is the case with certain varieties of rose. So are roses out then? Luckily not, because BBCT has teamed up with Roses UK to launch the award winning Sweet Haze, which is excellent for bumblebees!

It also helps to have a succession of flowers available for the bumblebees from mid-March to mid-October. Not only does this mean that the garden will look wonderful for most of the year, it also ensures that some rarer species of bumblebee, which tend to have shorter foraging ranges, can find food nearby all year long.

And if you are still stuck for ideas, "there are lots of other options on the BBCT website – www.bumblebeeconservationtrust.co.uk," suggests Robert Dawson.

What is BeeWatch, and how can members of the public get involved?

Surprising as it sounds, very little is known about the ecology of bumblebees: the distribution of the different bumblebee species, where they nest and how far an individual bee travels from its nest and what flowers and shrubs bumblebees are using.

Cue "BeeWatch", which is a project that everyone can get involved with and it contributes to this research. According to Lucie Southern, "we launched it last year and had nearly 7000 records, from Shetland to Cornwall. This year BeeWatch is already up and running and we have already received a sighting of the scarce red-shanked carder bee – a newly-listed UKBAP priority species."

Tips on identifying bees together with forms for recording sightings are available from the website and the organisation also have an email address for sightings: beewatch@bumblebeeconservationtrust.co.uk.

"Just email the picture (the emergence of digital cameras and camera phone has revolutionised how easy it is) with a location and date, and we’ll do our best!"

Big "Bee Six" Did You Know...?

1. That bumblebees have smelly feet. These chemical signals indicate where a flower has already been visited by a bee, improving foraging efficiency. It is also possible that bumblebee workers can ‘learn’ the smell of a good food source from a returning worker, and target that particular flower - they don’t have the expansive ‘waggledance’ of honey bees. Males, although they do no work, use other chemical signals to mark patches that they patrol in late summer and autumn, on the look-out for new queens

2. Bumblebees often live in nests underground.

3. Bumblebees make good neighbours. The queens and workers can sting, but very rarely do, so enjoy them but also treat them with respect. They only ever pose a problem when defending a nest.

4. Except for a few virgin queens, all bumblebees die each autumn.

5. There are 6 species of cuckoo bumblebee which were once like other bumblebees, but they have switched to a parasitic existence. The females kill or evict the queen and take over her workers as their own, using them to rear their own offspring. There are no cuckoo workers, only males and females.

6. Bumblebees have been discovered on Everest at heights greater than 5,600m above sea level. In recent scientific tests, some bees flew successfully in a flight chamber which recreated the thin air of 9,000m - a record for any insect species. (At 9,000m, air pressure is about a third of that at sea level so it is harder to fly - there is less air for wings to beat against).

And so, bees have colonised our cultural landscape completely: they have been used to sell everything from cereals to political ideology. Bumblebees, which are large, fuzzy and more colourful than honeybees or solitary bees, are also seen throughout popular culture: in books, cartoons and greeting cards. There are records going back 15000 years which document human fascination with bees. Let’s hope that this fascination can be translated into a real push to create a physical landscape ripe for them to thrive.

- June 2008

About the Author

Catherine Zentile is a member of the Quantum Matter research group in the Cavendish Laboratory at Cambridge University.