Ceratina cyanea can reach a length of 5–9 millimetres (0.20–0.35 in) (females) and 5–7 millimetres (0.20–0.28 in) (males). Head, chest and abdomen show a metallic blue colour. These bees have three submarginal cells in forewings, club-shaped antennae and a long thin tongue. The scutellum is densely punctured. The seventh tergite has a deep saddle and ends in two points.
Females nest in the vertical or slanted dead plant stems, such as thistles, blackberries (Rubus species), elderberries (Sambucus species) and roses. Then they provide the cells with a mixture of regurgitated nectar and pollen to feed the larvae. Adult males and females overwinter inside their cells into the stems. Often several insects spend the winter together.
- ^ a b Biolib
- ^ a b c d e f g h i Naturspaziergang
- ^ a b c d British Journal of Entomology and Natural History - Volume 8 - 1995
- ^ John L. Capinera - Encyclopedia of Entomology
- ^ a b  Révision des Xylocopinae (Hymenoptera : Apidae) de France et de Belgique
- ^ Felix Amiet, M. Herrmann, A. Müller, R. Neumeyer: Fauna Helvetica 20: Apidae 5. Centre Suisse de Cartographie de la Faune, 2007
- ^ a b c Essex Field Club
- ^ Global species