Flower-rich habitat boosts survival for bumblebees

The common carder bee foraging on red clover

At this time of year, bumblebee queens are a familiar sight foraging on spring flowers.

After spending the winter hibernating, they need to build up vital energy stores before laying their eggs.

According to the largest study of its kind, access to flower-rich habitats from spring through to summer is key to the survival of successive generations of the bees.

Scientists have discovered that bumblebees need flowers within a short distance (1km) of their colony.

Bumblebees are among the most important insect pollinators, yet they are in decline globally.

Until now, aspects of the lifecycle of bumblebees have remained a mystery, said ecologist, Dr Claire Carvell.

"Our research was looking to unravel some of these mysteries - and in particular to try and look at how the structure of habitats across a landscape, or the availability of flowers for the bees, affected this one key aspect of their life cycle, which was the survival of their families between years," she told BBC News.

The study tracked hundreds of mother, daughter and sister bumblebees across an area of farmland

The study, which took place in rural Buckinghamshire, is the first to track the effects of the surrounding landscape on wild bumblebees, from one generation to the next.

Researchers at the UK's Centre for Ecology and Hydrology sampled DNA from bumblebees of three different species. They reconstructed the family tree of hundreds of families of wild bumble bees across a large area of farmland.

They were able to match queen bumblebees to their daughters and sisters, to look at survival from one year to the next.

"What we found was that this survival between years of the bumblebee families was positively linked with the quality of the habitats surrounding their nests across that farm landscape," said Dr Carvell.

Even small increases in the amount of flowering plants through the spring and the summer could have a big effect, raising the survival rate of queen bumblebees by up to four times.

"They need to be carefully selected to provide pollen and nectar throughout the bumblebee's life cycle," said Dr Carvell. "And it's a combination of spring-flowering trees, crops such as willow and hedgerow flowers - even dead nettles and dandelions, for example.

"These are particularly important to getting colonies started in the spring and seeing them survive through to be successful into the next generation."

Plants for pollinators:

Wild plants

• Achillea millefolium (common yarrow)

• Cantaurea scabiosa (greater knapweed)

• Digitalis purpurea (common foxglove)

Garden plants

• Caryopteris x clandonensis (caryopteris)

• Dianthus barbatus (sweet william)

• Hesperis matronalis (dame's violet)

Source: RHS

The scientists found that as little as 1 to 2% of flower-rich habitat in a landscape, or even a garden or park, was enough to have a significant impact on populations of wild bumblebees.

Co-researcher Dr Matthew Heard said while there was an urgent need for more robust data on pollinator population decline, the study "strongly suggests that conservation interventions can have a lasting, positive impact on wild pollinators in agricultural landscapes".

Bumblebees are social insects, living in colonies. When the queens emerge in early spring, having spent the winter hibernating alone, they go out in search of food and a place to nest.

Each queen forms its own nest, lays its eggs, and produces a few hundred daughter workers.

Towards the end of the season, males and new queens hatch, which emerge from the nest to go in search of a mate.

Only fertilised queens go on to hibernate, after feeding heavily on pollen and nectar to build up fat stores.

The research is published in the journal, Nature.

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