Location of bumblebee nests is predicted by counts of nest-searching queens

Abstract

Bumblebee nests are difficult to find in sufficient numbers for well replicated studies. Counts of nest-searching queens in spring and early summer have been used as an indication of preferred nesting habitat, but this relationship has not yet been validated; high densities of nest-searching queens may indicate habitat with few nesting opportunities (meaning that queens have to spend longer looking for them).  From mid April 2010, queen bumblebees were counted along twenty transects in grassland and woodland habitats in Central Scotland, UK. The number of inflorescences of suitable forage plants were also estimated at each transect visit. The area surrounding each transect was searched for nests in the summer.   In total 173 queen bumblebees were recorded on transects, and of these 149 were engaged in nest-searching. Searches subsequently revealed 33 bumblebee nests.  The number of nest-searching queens on transects was significantly, positively related to the number of nests subsequently found. Estimated floral abundance along the transect did not correlate with numbers of nest-searching queens or the number of nests found, suggesting that queens do not target their searching to areas locally high in spring forage.   The data suggest that counts of nest-searching queens do provide a useful positive indication of good nesting habitat, and hence where bumblebee nests are likely to be found later in the year.