Bee energy budgets, not flower counts, put the forage gap in late July

Researchers at the University of Sussex have published a study in Functional Ecology that they describe as the first to directly measure the seasonal swing in the energy honeybees spend and gain while foraging ^[1][2]. Their answer is that the hard part of the year is late July and August, not spring ^[3][4], which puts most well-intentioned pollinator planting in the season when bees are already doing fine.

The method is the point. Instead of counting blooms and inferring supply, the team scored energy out from the time a bee spent flying and walking in a 60-second observation window, and energy in from the number and species of flowers visited and the nectar those flowers held ^[5]. That produced foraging data from 1,217 honeybees and nectar data from 1,426 flowers ^[6], collected from April to October at green spaces in and around Brighton and Edinburgh, including Arthur's Seat, the Royal Botanic Garden Edinburgh and Falmer village ^[7] - a seven-month window covering the active season ^[17].

Foraging efficiency was highest in spring, when insect-pollinated trees such as horse chestnut, willow and cherry are in bloom ^[9]. Shortage was most acute in late July and August ^[4]. The researchers attribute the dip to two things at once: fewer flowers in bloom and more active pollinators competing for them ^[10]. Brighton and Edinburgh, roughly 600 km apart, showed similar patterns, which the authors read as evidence that the late-summer squeeze applies across much of Britain ^[8].

Co-author Nicholas Balfour said the timing matters because late summer is when the vast majority of pollinator species are active and provisioning offspring ^[11]. Co-author Ciaran Harris argued the practical consequence follows directly: flowers that bloom when nectar is hardest to get are worth more than flowers that bloom when it is easy, and that can be achieved by planting late-summer bloomers, changing mowing schedules, or tolerating summer weeds such as thistle, ragwort and knapweed ^[12]. Read against the spring efficiency peak ^[9], the cheap version of that advice is the interesting one: the highest-value intervention is not buying plants, it is declining to cut things down in August.

Two caveats sit in the paper itself. Honeybees are a managed species being used as a landscape proxy; Harris justifies this on the grounds that they visit a wide variety of flower species and so indicate general nectar availability ^[14]. And the study covered green spaces in only two locations, which left the team unable to test how land use shapes nectar supply through the year ^[16]. Professor Francis Ratnieks said the direct energetic measurements confirm a pattern already emerging from indirect work in the same lab, including decoding bee dances to infer how far bees had to fly month by month ^[15].

The authors also note that heat waves reduce nectar in flowers and disrupt flowering times, on top of existing pressures such as agricultural intensification ^[13]. Watch for the land-use follow-up Harris flags, which is meant to test whether gardens and agri-environment farmland actually plug the seasonal gaps ^[16]. Until then, the operational takeaway is a date range, not a plant list.