Photo: Arnstein Staverløkk / NINA / CC BY 3.0

Osmia spinulosa

Spined Mason Bee

The smallest Osmia species in Switzerland (5–7 mm), with a black body, white ventral scopa, and distinctive sharp spines on the sides of the scutellum in females. Males have pale hair on the face and a less armoured scutellum. It is oligolectic on Asteraceae, especially thistles and knapweeds (Cirsium, Centaurea). It nests in pre-existing cavities in dead wood, hollow stems, and snail shells, sealing cells with chewed leaf pulp mixed with resin. In Switzerland it occurs in dry, warm habitats such as calcareous grasslands, dry meadows, and rocky slopes from lowlands to montane elevations. Swiss Red List: Vulnerable (VU).