Bumblebees – why they need your help

Bees 1There are a wide variety of bumblebees in the British Isles, collecting pollen from flowers to make honey.

  • The honeybee (Apis mellifera) is a social bee that forms large colonies that overwinter. It can be kept in hives and is the source of honey and beeswax. A strong honeybee colony may contain about 60,000 bees.
  • Bumblebees (Bombus spp.) are also social bees but their nests die out in late summer or early autumn. There are 23 bumblebee species in Britain but only about 12 are commonly seen in gardens. At peak strength in midsummer, a bumblebee nest may contain up to 200 bees.
  • There are about 265 species of solitary bee in Britain some of which are rare species confined to restricted habitats. Solitary bee nests are even smaller and with these non-social bees, each female constructs and provisions her nest on her own.

Many garden plants and agricultural crops need bees to bring about pollination by transferring pollen from the flowers’ anthers to the stigmas. These include most tree and soft fruits, and many vegetables including runner beans, broad beans, tomatoes, marrows and courgettes.

Over the past few year beekeepers and gardeners have noticed that bees are less healthy and there are fewer of them. If this trend continues, it could have serious implications, since most plants rely on bees and other insects to transfer pollen from one flower to another in order to germinate seeds.

Bees 2Why are bees in decline?
There is no one simple answer and the problems facing the honeybee are different to those affecting bumblebees and solitary bees.

Several factors have been identified as probable contributory causes of honeybee decline.

  • The Varroa mite a parasite that sucks bee blood from the bodies of honeybee larvae, pupae and adult bees. It evolved as a parasite of a South East Asian honeybee which has spread across the world.  It was first detected in Britain in 1992 and now infests bee hives throughout Britain and Ireland.
  • Honeybees and their larvae are affected by many diseases caused by bacteria, fungi and viruses. Some mite-transmitted viruses weaken honeybee colonies by reducing the longevity of adult honeybees. This affects their efficacy as pollinators and nectar gathers. Adult honeybees that develop in late summer will normally overwinter in the hive and survive until the spring. Those weakened by viruses die prematurely. A colony that appears strong in late summer can die out over winter or is reduced by the spring to a greatly weakened and non-viable colony.
  • Honeybees today need more care and management because of the need to prevent damaging levels of Varroa mites building up. “Leave alone” beekeepers will lose their bees. In early autumn, it is important to ensure honeybees have enough honey in their hives to keep them going until nectar becomes available again in the spring. Hives that have insufficient honey must be fed with sugar solution to top up their stores.
  • Pesticides, especially insecticides, are often blamed for bee losses.

Bumblebees and solitary bees are not attacked by Varroa mite. The main problems affecting them are loss of suitable habitat:

  • Some bumblebees and solitary bees collect nectar and pollen from a restricted range of plants. These are usually wild flowers, so garden plants are of no benefit to them. Traditionally managed flower-rich meadows, are now a rare feature of the British landscape and this appears to be a contributory factor in the decline of some bumblebee species. Where suitable habitat remains, it is often fragmented, making it more difficult for bee populations to expand and colonise new areas.
  • Some bumblebees and solitary bees have specific requirements for nest sites. The loss and fragmentation of suitable habitats reduces nesting opportunities.

How can you help?

  • Bees need pollen and nectar, both of which are most plentiful in wild flowers and traditional cottage garden plants. The crucial thing is to provide this resource as early in the year as possible (even snowdrops can help on warm days in January).
  • You could set aside a border to make a hay meadow, with plants such as clover, sainfoin, bedstraw and vetches.  Honeybees are active from late winter to autumn, so try and have bee-friendly plants in flower for as much of that time as possible. Use pesticides sparingly. Those based on fatty acids or plant oils and extracts pose little danger to bees but will not control all pests. Avoid spraying open flowers and if possible do spraying in the evening when bees are less active.
  • Provide nest sites for solitary bees: Some will nest in hollow stems, such as bamboo canes or herbaceous plant stems. Hole diameters in the range 2-8mm are required. Cardboard nest tubes can be bought in garden centres. Holes 2-8mmdiameter can be drilled in fence posts or logs. Place these nest sites in sunny positions. Some solitary bees nest in the ground, either in bare soil or short turf. They will find their own nest sites, so tolerate the small mounds of soil deposited by the female bees when they excavate their nest tunnels. Bumblebee nest boxes can be purchased but they are often ignored by queen bumblebees. They prefer to find their own nest sites down tunnels dug by mice or in grass tussocks.

Find out more at www.bumblebeeconservation.org.uk