Research news

Letting late summer weeds grow could help honeybees when they find it most challenging to gather nectar, according to new research from the University of Sussex.  

Researchers have found that honeybees find it hardest to forage fornectar in late summer, particularly in August. Their study, published in the British Ecological Society Journal, Functional Ecology is the first to use thenovel method of directly measuringseasonal changes in the energy honeybees expendand gain from foraging. 

Conducting their study in green spaces in and around Brighton and Edinburgh, the researchers found that food shortages were most acute in late July and August, suggesting that in these months, bees found it the most challenging to gather nectar. 

The researchers suggest that this is likely due to fewer flowers in bloom in late summer and a higher number of active pollinators competing for these flowers. This contrasted with spring when honeybee foraging efficiency was at its highest, a time when most insect-pollinated trees like horse chestnut, willow and cherry are in bloom. 

Dr Nicholas Balfour, a co-author on this study, said: “Our findings add to a growing body of literature indicating that late-summer is a particularly challenging season for pollinators. This is incredibly important, as this period of the year is when the vast majority of pollinator species are active and require forage to provision for their offspring.” 

Dr Ciaran Harris, also a co-author on this study, added: “Encouraging flowers that bloom in late summer when bees find it more challenging to gather nectar or pollen will be more valuable for helping them.This could be achieved by planting late-summer blooming flowers, adjusting when lawns are mown, or being more tolerant of summer-blooming 'weeds' like thistle, ragwort, and knapweed.” 

Refraining from removing late summer-blooming weeds could be especially important  when heatwaves are reducing nectar availability in flowers and disrupting flowering times, potentially exacerbating existing pressures on pollinators such as agricultural intensification. 

The findings from the study have implications for other pollinators too. Dr Harris said: “Late summer is likely challenging for other species of flower-visiting insects because honeybees visit a large variety of flower species. This means that they’re a good indicator of overall availability of nectar in the landscape.” 

In the study, the researchers directly observed honeybees foraging at sites across Brighton and Edinburgh, including Arthur’s Seat, The Royal Botanic Gardens Edinburgh and Falmer village from April to October. 

To determine the foraging success of honeybees at different times of year, the researchers compared the energy expended during foraging (calculated by the amount of time spent flying and walking in a 60 second period) with energy received from foraging (calculated by the number and species of flowers visited and the quantities of nectar). 

Over the course of the study, the researchers collected foraging data from 1,217 honeybees and nectar data from 1,426 flowers. 

They found similar patterns in Brighton and Edinburgh, despite the cities being ~600km apart. This suggests that late summer might be a challenging period for bees to gather food in many areas of Britain. 

Professor Francis Ratnieks, a co-author on this study, said:“What is particularly satisfying about this project is that it directly measures the energetic profitability of nectar foraging across the active foraging season. 

“The results confirm the pattern that had emerged from a wide range of indirect studies done in our lab,which included decoding bee dances to see how far they had to fly to forage month by month. These studies all point to late summer being the most challenging season for gathering nectar, and in doing so simplify the task of ‘helping the bees’”.