Patterns of nest-site selection by Colletes thoracicus within a forested watershed

Despite the importance of suitable nesting habitat for bee conservation, the nesting requirements of most species remain unknown. We sought to better understand the distribution of Colletes thoracicus Smith (Hymenoptera: Colletidae) nesting aggregations within a forested watershed in GA, USA. We found 13 and 17 aggregations within the watershed in 2022 and 2023, respectively, and seven of these occurred at the same locations between years. The aggregations were found exclusively along the banks of stream channels and, compared to randomly selected non-aggregation sites, were associated with sandier and drier soil and with the presence of the herbaceous perennial, Podophyllum peltatum L. We suggest that the association with P. peltatum may result from favorable disturbances to the litter layer caused by the springtime emergence of the plant. Our results demonstrate that closed-canopy forests, and especially the sandier soils bordering streams, can provide suitable nesting sites for C. thoracicus and possibly other ground-nesting bee species.