Osmia bicolor

It is mainly a central European species that becomes rare and sporadic north of Belgium, with a range from southern Finland to Spain and east to the former Yugoslavia and Romania.

In Britain it is found mostly in southern England and south Wales, and its range closely follows chalk and limestone soils.

Typical habitat is calcareous grassland and open deciduous woodland on chalk and limestone soils.

The males are among the first solitary bees to appear in spring, and the species has one generation a year flying from April to early July.

The species overwinters as an adult inside a self-spun cocoon within its brood cell.

Females nest in empty snail shells, including those of the Roman snail, banded snails of the genus Cepaea and the Kentish snail.

Cells inside the shell are separated by thin partitions of chewed leaf pulp from plants such as cinquefoil, strawberry, willow and rose.

The nest plug is a 1 to 2 cm space densely packed with small pebbles, earth crumbs, broken snail shells, chalk or wood particles, closed by a final leaf-pulp partition.

Provisioning a single cell takes 27 to 39 foraging trips, and nests hold mostly one or two, rarely up to five, brood cells.

It is polylectic, with pollen sources recorded from many plant families including carrot, asparagus, daisy, borage, cabbage, pea, mint, rose, willow and violet families.

Flowers visited in Britain include wood anemone, bluebell, bird's-foot trefoil, horseshoe vetch, sainfoin, sallow, ground-ivy, daisy and dandelion.

Once the shell is closed the female turns it so the opening faces the ground, then covers it with hundreds of pine needles, dry grass blades or fragments of dead leaves.

Males keep to small home ranges, patrolling flowers and snail shells on the ground along roughly fixed circular routes, and sleep singly or in small groups inside empty snail shells.

Known nest enemies include the cuckoo wasps Chrysura cuprea, C. refulgens and C. trimaculata, the parasitoid Eulophus osmiarum and the sapygid wasp Sapyga quinquepunctata.