Bumblebees

What are Bumblebees?

Bees are insects (they have 6 legs, and wings as in most insects).
Bumblebees are social bees which live in colonies, each with a queen and workers. New colonies are formed each year. (Hive-bees form very large semi-permanent colonies, building up a food reserve to keep them over winter. The queen lives for several years.)
They are quite large and furry, and mind their own business. To many people they are regarded as nice and friendly, and useful.
Their job in the web of life is to pollinate flowers, and they are jolly good at it since they can operate in much lower temperatures and in poorer light than most other bees.

Red-tailed carder-bee (Bombus ruderarius)
© Ben Hamers
The queens and workers can sting, but they have to be very severely provoked such as by grasping them between fingers. Whereas a hive bee leaves its sting in a victim, with accompanying venom sac, bumblebees withdraw their sting so that the sensation is of a sharp needle, and for most people a residual pain and slight inflammation that fades after a short time. Males have no sting.

How they live

Only the queens survive the winter, hibernating underground in a dug out cell, under leaf litter or inside rotten wood.
In the spring, the queens make a nest. For those that nest underground, an old mouse nest down a burrow is perfect. Carder bumblebees nest on the surface, gathering moss or plant debris into a ball with a hollow centre.
The queen forages at flowers, drinking nectar and gathering pollen. Her fur becomes dusted in pollen which is combed-off into pollen baskets on her back legs.
Different species of bumblebee have their own flower preferences. Those with an extra long tongue visit flowers with deep nectaries.
The foraging distance from the nest can be half a mile or more.
Some insects, particularly hoverflies, are very good mimics of bumblebees. Birds and other insect predators soon learn that bumblebees sting if grabbed as food, so leave them alone. A hoverfly mimic looks dangerous when in fact it is harmless. Bees have long cylindrical antennae, but the look-alike hoverflies have very short antennae.
At the nest, the queen (and later the workers) stores some of the nectar in a wax honey-pot. Thus there is a larder in case the weather is bad or for a poor flower day. Later, newly emerged adults can have a drink to buck-up their energy.

White-tailed bumblebee
(Bombus lucorum) © Roger Key
The queen lays eggs in a pollen lump. When full grown, these grubs pupate and then hatch as worker bumblebees which are smaller than the queen. Workers are infertile females, and their sole task is to work for the communal good of the nest.
With a work-force, the provisioning of the nest increases. The queen is now able to stay at home, laying more eggs and supervising the nest. Several more generations of workers are produced, the oldest ones dying after about 2 months of intense activity.
When the work-force has built-up to good strength, though often still less than 200, the queen lays special eggs which hatch into grubs which grow extra large. These will become the fertile next generation of queens and males.
The new queens and males leave the nest to mate. The males then die, and the nest peters out since the worker population is no longer being topped-up with replacements.
Most bumblebees nest once a year but a few species can manage two generations in a season.
Because bumblebees are active from spring to late summer, they have to seek out a range of different suitable flowers as the season progresses. This is the Achilles Heel of bumblebee life style, since any break in sufficiency of their flowers spells disaster.
Remarkably, some species of bumblebees are cuckoos. Instead of making its own nest, the female takes over the well established nest of another species. The cuckoo stings to death the resident queen and then has the workers rear its own next generatiion of fertile females and males.

Garden bumblebee
(Bombus hortorum)
© Roger Key

The British Fauna

There are about 25 species that are listed in the British fauna, of which 6 are cuckoo species

Additionally there are geographically distinct populations, especially on the coast and islands of west and north Scotland, some of which may be treated as subspecies.

Three species are believed to be extinct in the UK; the Apple bumblebee (Bombus pomorum), Cullem's bumblebee (Bombus cullumanus) and most recently, in the early 1990s, the Short-haired bumblebee (Bombus subterraneus). Other bumblebees have suffered many local extinctions in recent decades, for instance while the Great yellow bumblebee (Bombus distinguendus) hangs on in North West Scotland but is extinct in England and Wales.

Many bumblebees are now rare or very localised.

The majority of species prefer the warmer climate of the south of the UK, fewer species occurring in cooler northern and upland districts where cloud and rain are limitations on foraging. However, a few species prefer the north.

The Tree bumblebee (Bombus hypnorum) has recently established itself in southern Britain and others may also come from continental Europe if global warming continues.

Conservation

Bumblebees have undergone a massive decline since the 1950s, in fact one of the most severe declines of any group of wildlife in Britain.

One reason is that as colonial social insects, population density of nests is low since each nest needs a large viable radius of foraging.

Thus a small piece of habitat is not enough. For most bumblebees we have to be talking of landscape scale conservation and metapopulation structure. A metapopulation is one composed of linked separate populations, any one of which may die out but can be recolonised; genetic flow is also crucial.

On the whole the short-tongued bumblebees have survived best, whilst the long-tongued species have suffered the most severe crashes in status. The specialisation of the latter means that they have the advantage of least competition for deep-nectar flowers, but the penalty is that they are in major trouble if such flowers are not sufficiently available throughout the season.

Recent studies have revealed the importance of meadows with wild red clover (no longer widespread in rural areas), and of such flowers as white dead nettle along hedgerows and on urban 'waste' ground.

Availability of nectar sources

Since a nest colony has to remain fully provisioned over several months, any disruption of supplies of nectar and pollen spells doom:

Flowers may be present but of the wrong sort.
Suitable flowers may be present for only part of the nesting period.
A good source may be suddenly cut-down or ploughed up.
A dose of weedkillers along hedgerows or in fields kills all the flowers.
Or the bulldozers move-in to make way for new development.

Loss of habitat

Rough grassland with flowers and nest sites might be planted with trees (not always good for wildlife!), thus leading to the ground becoming too shaded.
Progressive land management changes or development reaches the threshold whereby a bumblebee population collapses.

Much of the British landscape has become intensely managed by modern agricultural practices.

Weed/flower free crop monocultures have replaced crops with weed flowers. Fertilisers have replaced the necessity to leave land fallow on rotation.
Pesticides are a recent, but now abundant, addition to the environment
Highly fertilised grasslands drastically impoverish the flora.
Very extensive field drainage, with resultant loss of marsh flower options.
Hedgerow flower and nest sites ripped-out on a vast scale, and those remaining often ploughed hard up to the edge and too regularly mechanically cut.
Roadside verges narrowed as roads are widened, and verges often cut just when flower resource are coming to optimum.

Forest practice has changed:

Extensive areas of coppice woodland have been neglected as no longer commercially viable, so the rotational continuity of woodland glade and ride flowers has gone.
Coniferisation of deciduous woodland has suppressed and often simplified the flora.

In urban areas:

Green space has become over-tidy and manicured, with grasslands regularly cut and scruffy ground eliminated or planted with trees.
Brownfield land ('waste' and other undeveloped land), often the last oasis for many invertebrates, is being built-over as rapidly as possible as a matter of government policy.
Gardens are planted with modern breeds of plant that are no longer able to produce nectar.
Much modern housing allocates very small gardens, and blocks of flats have token plantings at best, resulting in either over-tidiness or over- neglect. Fads in garden planting may diminish the supply of bumblebee friendly flowers.

There are many things that can be done to help bumblebees to flourish.

The gardener can plant suitable shrubs and herbs, and provide artificial nest sites.
The manager of urban open spaces can review cutting regimes and planting plans to see if wild flowers might be given more encouragement. Nesting areas of rough grassland and hedges may need more sympathy.
The planner needs more appreciation of the importance of brownfield land, and of the less manicured landscapes on the urban fringe and in rural areas. Bumblebees need district planning; they cannot remain viable on 'pocket-hankerchief' token fragments of land in isolation.
The farmer is already being encouraged to be more wildlife friendly, as indeed many are. Bumblebees do not need any extra measure beyond the well expounded public desire to encourage more wildflowers and greater appreciation of hedgerows and ditch margins. The concepts of headlands and beetle banks fit in well.
The industrialist and developer need to recognise that not all 'waste land' is equal, but some is especially important to bumblebees and other wildlife. With better anticipation and dialogue, at least some of the clashes of interest can be avoided.
In local government, note the Local Biodiversity Action Plans are supposed to maintain, enhance and re-create those habitats and species of special significance, and total biodiversity for that Local area. Bumblebee needs have generally been neglected, so far.
In national government (and national devolved authorities), policies towards brownfield land need urgent review, together with other policies affecting urban wildlife. Rural landscape policies need to be bumblebee friendly.
Just as important, conservation site managers need to recognise that for the most part they have scarcely begun to address the question as to whether bumblebee populations are helped or hindered at present.

Studying and recording

The Bees, Wasps and Ants Recording Society is the lead group encouraging the study and conservation of bumblebees.

The Biodiversity Action Plan treats bumblebees as a priority group. As 'flag-ship' species, five bumblebees have Species Action Plans, an exceptionally high proportion of the British fauna.

A Bumblebee Working Group has been carrying out the research required, including projects within the English Nature Species Recovery Program.

Among the project proposals is one to involve public participation in recording the current distribution and status of bumblebees, for which Buglife is seeking funding. Bumblebee public participation project

Common carder-bee Bombus pascuorum ©Roger Key