Females usually about 10–12 mm long.
Fine-art photographic collection
Osmia bicornis
A mason bee whose female uses two facial horns as tools while building a mud-walled nursery.
About this species
Osmia bicornis(Linnaeus, 1758)
Information reviewed15 July 2026
Osmia bicornis is a spring-flying solitary mason bee that nests in pre-existing cavities. Each female constructs a row of brood cells, provisions them with pollen and seals the partitions with mud.
Taxonomy
Animalia · Arthropoda · Insecta · Hymenoptera · Megachilidae · Osmia
Accepted taxon. · checked 2026-07-15
Europe and western AsiaBroad range and selected reference localities — not a complete occurrence map.
Europe and western Asia
Gardens, orchards, woodland edges and buildings with cavities, hollow stems or nest tubes.
Diurnal in spring, often active in cool weather.
Adults take nectar; females collect pollen to provision larvae.
Solitary.
What makes this species remarkable?
The female’s two forward-pointing facial horns are working tools used while carrying, pressing and shaping wet mud inside the nest.
She places daughters in larger, deeper cells and sons nearer the entrance; the males emerge first and wait for females in spring.
A single female builds a linear apartment block of mud-walled cells, sealing one pollen loaf and one egg into each private chamber.