[2] Osmia parietina is associated with areas of unimproved grassland, where their primary nectar source bird's foot trefoil (Lotus corniculatus) grows.

Females build their nests inside the crevices of drystone walls, rock faces and standing deadwood.

[1] Although L. corniculatus is the primary nectar source for Osmia parietina, it has been recorded visiting flowers of other plant species such as: Ajuga reptans, Hippocrepis comosa, Rubus fruticosus, Sedum reflexum, Trifolium pratense and Veronica chamaedrys.

[2] The Western mason bee is also one of several host species for the parasitic Northern Osmia ruby-tailed wasp (Chrysura hirsuta).

The loss of sunny rock habitats for the bees to nest in due to shrub encroachment also threatens the species.