Nest architecture of Osmia nigriventris. 7–9) Nest seals of nests 19, 16 and 18. 10) Five-layered nest plug of nest 18. 11) Single-layered nest plug of nest 17. 12) Ring-shaped threshold. 13, 14) Three-layered cell partitions. 15) Brood cells with larval provisions. 16) Brood cells with larval cocoons.