Over the last five years we have been managing some of our grassland for bumblebees, and every year between May and August we have also been counting the bees to monitor the effects. Recently we summarized this data and over all, things are looking pretty good! Over the first four years of the project, numbers rose steadily from around 300 in 2014 to 900 in 2017. Numbers did drop back this year, though this is likely due to the very hot and dry summer conditions and their effect on the ability of forage plants to produce pollen and particularly nectar.
The chart below shows the numbers for individual species over the years. One of the most gratifying aspects has been the increase in numbers of moss/brown-banded carder bee (it's not always possible to tell the two species apart in the field so they are treated together). These are two of a suite of rare species that the management is really aimed at, the others being red-shanked carder bee and large garden bumblebee, both of which have also been recorded on our 'bumblebee fields' in the last five years (though in very small numbers and not always on the transects).
The data has also allowed us to look at the range of forage species used and the different preferences bumblebee exhibit in using them (shown in the chart below). Legumes are an important pollen source for many bees, providing a protein rich food for developing larvae and the chart shows the importance of species such white clover, red clover and birdsfoot trefoil at Rye Harbour, while species such as viper's bugloss, creeping thistle and common ragwort are also important, probably as nectar sources. The chart also shows how bees differ in their foraging habits. Red-tailed bumblebee, for instance, loves white clover, birdsfoot trefoil and common ragwort, making up a large proportion of the foraging individuals for these two species, while red-clover is preferred by moss/brown-banded carder and common carder.