Large-headed resin bees (Heriades truncorum) make their nests in a pre-existing cavity in wood. You can create suitable nesting sites by drilling holes in blocks of wood like this one we saw at John Little’s house a few years ago. He runs the Grass Roof Company and has pioneered incorporating nest sites for solitary bees on roofs and walls. He uses his own home and gardens as a test bed.
After she has laid her eggs in the cavity, this robust. solitary bee plugs it with tiny bits of grit and stone she collects and then glues it all together with resin collected from nearby trees. Here’s the bee in action…it’s like fitting together pieces of a jigsaw, or making a mosaic – quite amazing!!! And the next generation of resin bees have to break through the ‘door’ when they emerge next year.