Horned mason bee
Osmia cornuta
The horned mason bee is one of the earliest wild bee species to emerge in spring in Central Europe. It is characterized by a jet-black thorax and a bright reddish-orange abdomen. Females possess two distinct small horns on their clypeus, which gives the species its name. It is an extremely efficient pollinator for fruit orchards and frequently inhabits artificial nesting aids in gardens.
Details
Identification
Rusty red abdomen, black thorax, females with two small horns on the clypeus, males with a white facial mask and longer antennae.
Social behavior
Solitary living, does not form colonies, but often nests in high densities (aggregations) at suitable sites.
Diet
Polylectic, visits about 14 plant families, but prefers Rosaceae (fruit trees) and Salicaceae (willows).
Spawning substrate
Cavities such as beetle burrows, reed stalks, or holes in wood; sealed with mud.
Overwintering
Overwinters as a fully developed adult insect (imago) inside a cocoon within the nest cell.
Ecology
Ecological role
Important pollinator of early-blooming plants; active at significantly lower temperatures than honeybees.
Natural predators
Birds (woodpeckers, tits), parasitic wasps, bee flies, and fruit flies (Cacoxenus indagator).
Competitor species
Other mason bees such as Osmia bicornis (Red mason bee) regarding nesting sites.
Ecosystem service
Pollination of crops (apple, pear, cherry, almond) and wild plants.
Threats
Lack of food sources due to monocultures, pesticide use in agriculture, and loss of natural nesting opportunities.
Scientific profile
Profile
Distinguishing features
Females possess two distinct, forward-pointing horns on the clypeus (giving the species its name). The species is significantly larger and more robust than the related Osmia bicornis. Males have longer antennae and a white facial tuft.
Habitat
Open landscapes, orchards, forest edges, and especially urban areas (gardens, parks, cemeteries).
Protection & threats
Main threats
Lack of suitable nesting sites due to building renovations, use of broad-spectrum insecticides in agriculture, and lack of early-blooming forage plants in cleared landscapes.
Population trend
Stable to increasing; the species benefits significantly from climate warming and the provision of artificial nesting aids in urban areas.
Conservation measures
Preservation and creation of orchards, provision of nesting aids, promotion of mud patches in gardens, and planting of native early bloomers (especially willows).