Wasps

In addition to nesting bees, we often see wasps choosing our nest blocks to make their homes. Like our nesting bees, these nesting wasps are solitary, with a single female building each nest. Unlike bees, which provide pollen for their offspring to eat, wasps provision each nest cell with insect or spider prey for their larval offspring. Solitary wasps often use similar resources as bees, like resin and mud, to construct their nests, but some are much more noticeable, like our common grass-carrying wasps (Isodontia). 

Parasitic wasps also enter our nest blocks, through a range of relationships with nest-building species. Parasitic wasps may lay their eggs directly in the host nest or lay their eggs on a different insect that is brought to the nest as prey. Parasitic wasps are a fascinating and normal part of a healthy insect community. However, some parasitic species can get overpopulated in bee blocks if they aren't cleaned regularly, especially in places where many bee blocks are located together.