What features of sand quarries affect their attractiveness for bees?

Conservation of organisms usually focuses on areas that are not significantly altered by human activity. However, many areas under the influence of human activity can be important for maintaining biodiversity. Sand quarries became important substitute habitats for many species of insects, including wild bees. However, their attractiveness as a potential place for oligolectic bees to forage is insufficiently known. We examined the species richness and abundance of wild bees, including species with a specialized diet, in 20 used and inactive sand quarries differing in area (0.64-7.40 ha), succession stage and location in the landscape. Some of the inactive quarries were littered with municipal and household waste, i.e. mainly plant biomass and soil from home gardens and construction debris. We recorded 156 species of wild bees (32% of the domestic Polish fauna). Polylectic species accounted for 57% of the bee community (66% of the total abundance), 17% of the community were oligolectic species (25% of the total abundance) and 26% of the community were cleptoparasitic species (9% of the total abundance). The total number of polylectic species and their abundance increased with the increasing area of sand quarries. At the same time, the richness and abundance of oligolectic species increased with the increasing number and abundance of food species. Among the recorded oligolectic bees, 55% were common in the studied habitats, 30% were frequently reported, and only 15% were rare species.