Genus: Osmia Panzer, 1806
Subgenus: O. (Osmia) Panzer, 1806
Species: Osmia bicornis Linnaeus, 1758
Common name: red mason bee or red mortar bee
Osmia (Osmia) bicornis are black bees with a metallic blue to blue-green shimmer (Amiet et al. 2004). Females have black hair on their face, and two distinct horns projecting from their hairless clypeus. They have brown-gray hair on T1–T3 and black hair on T4–T6 (Amiet et al. 2004). Male hair coloration is similar to the females with exception of abundant whiteish-yellow hairs on their face and clypeus, and T4–T7 have black hair. Female body length ranges from 8–12 mm; male body length is 8–12 mm (Amiet et al. 2004).
Osmia bicornis look similar to O. rufina and O. pedicornis. Females of these species all have lateral horns and bidentate median apical projection on the clypeus. O. rufina females can be differentiated by the shape of the median apical projections on the clypeus and the long, non-bifurcate lateral horns on the clypeus. Males are similar in size and hair color and can be difficult to distinguish without dissecting them to see the genitalia and hidden sterna. They can, however, be distinguished by the shape of S8 and the apex of the gonocoxites.
Osmia bicornis are generalists and have been observed pollinating a variety of plant species (Amiet et al. 2004). They do, however, seem to prefer plants within the Rosaceae and Fabaceae families (Banaszak and Romasenko 1998). O. bicornis are also especially efficient at pollinating apple and some crops grown within greenhouses (Krunic et al. 1995).
Osmia bicornis nest in a wide variety of preexisting cavities including wooden buildings, pithy or hollow stems, thatched roofs, snail shells, and man-made artificial nests (Banaszak and Romasenko 1998). Cells are usually arranged linearly in deep narrow cavities but are sometimes laid flat or in multiple rows in shallow wide cavities (Banaszak and Romasenko 1998; Amiet et al. 2004; Ivanov 2006). Cell partitions and nest plugs are comprised of moistened soil or clay (Banaszak and Romasenko 1998).
Osmia bicornis specimens have been recorded across Europe, northern Africa, and western Asia (Amiet et al. 2004).