February 2023 - A house of straw
The sight of three large, healthy, queen Buff-tailed bumblebees foraging together on an early flowering Daphne odora last month, was a wonderful experience. Not only was it reassurance that these pollinators had survived the worst of the weather of the last 6 months, but also because it was proof that these individuals had independently found safe hibernation sites close to the location of this flowering shrub.
This species is one of the earliest to emerge in the Spring and will be visible feeding on flowers that are small, shallow and open because their tongues are relatively short and cannot reach into the depths of more complex blooms. The rest of their waking hours will be spent flying low over the ground looking for suitable concealed nest-sites that are safe from invasion by birds and mice, and that are sheltered from the sun. Keeping the nest cool at the height of Summer is more demanding than keeping it warm at lower temperatures.
Once one starts to take an interest in pollinators, one learns of nests in compost heaps, under garden sheds, in stone walls, trees, and grassy banks. Last month I described how to make an underground nest-site using a bird-box and twigs. This approach was successful in a local allotment, but the general rate of uptake is nationally only about 3%. However, an important scientific paper from Sweden recently reported a study on the use of straw bales by bumblebees when setting up home.
For decades, Swedish farmers have put bales into fields where they were growing red clover in the belief that it was good for the harvest. Researchers looked at the number of bumblebee nests in 1255 bales on 58 farms. The farmers put bales against walls, hedges, stone banks, in the open, or against farm implements. At the end of the study they found that no nests had been made in their arable fields in the absence of bales whereas 41% of bales in comparable locations had nests. A range of bumblebee species, including a rare one, had chosen to use the bales. Partially degraded bales were used more often than new ones.
This approach is much more acceptable to farmers than giving over productive acreage to wildflower meadows. The findings show the potential benefits if we add bales to waste ground on farms, gardens, allotments, playing fields, golf-courses, church yards, public parks, National Trust land, etc. It is effective, cheap, convenient, and widely applicable.
The Wild Cookham website here has useful descriptions and pictures of UK bumblebees and copies of previous months' newsletters.
Adrian Doble (Bumblebee Conservation Trust volunteer) February 2023