Worcestershire Record No. 6 April 1999 p. 20

BUMBLEBEES ENDANGERED

When did you last see a bumblebee foraging in your garden?

Some of you who listen to the Today programme on Radio 4 may have heard the broadcast on Monday 8th March when George Else of the Bee Wasps and Ants Recording Society (BWARS) outlined the alarming state of our bumblebee populations. The following notes summarises the main points that emerged from discussions at the Bumblebee Working Group seminar held on 12th February 1999 There has been a catastrophic decline (and possible extinction) of some species over recent decades. Even formally common species are declining dramatically. Of the 16 species of bumblebee that occur in the British Isles only 6 species remain relatively common and widely distributed. Similar declines have been reported from continental Europe.

Nest densities of some more threatened species may be as low as one or two per square kilometre! The problem is on a large landscape scale.

The reasons for the declines vary from species to species and are due to a variety of factors but the most significant overall reasons are the loss of foraging and nesting habitat through agricultural intensification.

One of the most critical changes in the farmed landscape is the reduced availability of suitable forage flowers, especially those with long corollas and a high nectar load eg legumes and labiates. Many of the most important forage flowers are still widespread and common, eg red clover and bird's-foot trefoil. However, they may not be present in sufficient quantity over wide enough areas throughout the forage season that is. the whole summer.

Many bumblebees require tall, tussocky yet open swards for nesting. These need only occasional grazing or cutting ( every two or three years), or may be more extensively grazed at low-intensity on a more regular basis. Unlike most solitary bees bumblebees are not associated with warm, dry, sparsely vegetated sun-baked slopes. Intensive winter grazing may harm species which hibernate in tussocks or moss clumps.

The current agri-improvement schemes such as set-aside and conservation headlands may only offer limited respite. Most schemes are too short-term and do not cover a wide enough area. There is an urgent need for large scale changes to the farmed landscape with a reversion to more extensive systems. 

Bumblebees in Britain

Bumblebees have evolved in temperate regions and, unlike many solitary bees survive well in cool environments and like hive bees, are able to temperature regulate their nests. They have longer flight periods than solitary species and are not specialised to forage at single flower species, however they do have marked preferences for particular flower families and require a high intake of energy giving nectar. Flowers with long corollas provide such a source.

Bumblebees can be roughly divided into two groups: short- and long-tongued. It is most of the longer tongued species that depend on flowers with a long corolla, especially labiates and legumes. Nectar availability is often a limiting factor in nest success, particularly when queens and males are being reared. The decline of most species has been linked to the reduced availability suitable flowers for nectar and pollen. Foxgloves and vipers bugloss are frequently visited but being biennial, their abundance can vary greatly from one year to the next. Red clover, a component of many unimproved meadows, is another important forage source. It has a long flowering period and flowers well after cutting or grazing. Other important species include bird's-foot trefoil, red bartsia and black knapweed. Hedgerow plants like white deadnettle, hedge woundwort, tufted vetch and bush vetch are also valuable. Modern seed mixes often only contain white or hybrid clovers that do not have long corollas and only produce small quantities of nectar.

Extensive sowing of legume crops, e.g. sanfoin and red clover would benefit many species. Large scale clover meadow restoration is planned in Wiltshire this year by one sympathetic farmer.

Of the sixteen species of bumblebee recently recorded in the British Isle only six remain widely distributed and frequent in occurrence, most others have undergone dramatic declines since the 1950's. Mainly due to loss of foraging and nesting habitat as outlined above.

There are five species included in the UK Biodiversity Action Plan Programme: