Mason. Nesting site: Exposed nests built in depressions, cracks or surface irregularities of stones and rocks; in small cavities in rocks and stones with 1-3 cells; insect burrows in the soil. Nesting material: Cell walls and nest plug made of mud; no pebbles are used as for example in H. anthocopoides. (Benoist, 1931; Le Goff, 2004, personal observation)