Chalybion, also known as blue mud-dauber wasps, is a genus of wasp in the family Sphecidae. The species often nest in old, abandoned mud nests of other species and in pre-existing cavities.

Taxonomy and phylogeny Chalybion was originally described as a genus by Dahlbom in 1843. Kohl demoted Chalybion to a subgenus of Sceliphron in 1918 and established Hemichalybion as a sister subgenus of Sceliphron. Both Chalybion and Hemichalybion were elevated to genus status by Bohart and Menke in 1963. The same authors then demoted Hemichalybion to a subgenus of Chalybion in 1976.

Distribution and habitat Chalybion species are present in all continents except for Antarctica though are most common in the Nearctic and Paleotropic regions.

Behavior Females of Chalybion species nest in a wide range of natural or artificial pre-existing cavities, such as holes in stone, wood, in walls, and in plant stems. They also reuse old mud nests of other wasps, including those of Trypoxylon, Sceliphron, Eumeninae, and Ageniellini, or old mud nests of bees.

C. californicum in particular is known for repurposing old nests of Sceliphron caementarium. The females then hunt and paralyze spiders, particularly of the families Araneidae and Theridiidae, which they use as provisions their brood cells.

Interaction with other species The nests of Chalybion may, themselves, be repurposed by other mud-nesting wasps, such as Eumeninae.

Species There are 54 described living species of Chalybion:

Subgenus Chalybion (Chalybion) Agassiz, 1846 Chalybion fuscum (Lepeletier, 1845) (Madagascar, Sri Lanka) Chalybion ohli Dollfuss, 2016 Chalybion yangi Li, 1995

Chalybion bengalense species-group Chalybion bengalense (Dahlbom, 1845) (Hawaii, Mauritius, Mozambique, Seychelles, Socotra, South Africa; introduced in Italy) Chalybion clarebaltazarae Abenis & Lit, 2020 Chalybion flebile (Lepeletier de Saint Fargeau, 1845) Chalybion japonicum (Gribodo, 1880) (China, Japan, Ryukyu Islands, South Korea, Tanzania, Thailand) Chalybion klapperichi (Balthasar, 1957) Chalybion minos (de Beaumont, 1965) Chalybion omissum (Kohl, 1889) Chalybion petroleum Hensen, 1988 Chalybion saudiarabicum Schmid-Egger, 2025 Chalybion stephenreyesi Abenis & Lit, 2020 Chalybion turanicum (Gussakovskij, 1935) Chalybion vechti Hensen, 1988 Chalybion walteri (Kohl, 1889) Chalybion zimmermanni Dahlbom, 1843 (North America) Chalybion zimmermanni zimmermanni Dahlbom, 1843 Chalybion zimmermanni aztecum (de Saussure, 1867) Chalybion zimmermanni peninsulare R. Bohart and Menke, 1963

Chalybion californicum species-group Chalybion californicum (de Saussure, 1867) (North America; introduced in Croatia)

Chalybion fabricator species-group Chalybion accline (Kohl, 1918) Chalybion fabricator (F. Smith, 1860) Chalybion hainanense Terayama & Tano, 2018 Chalybion lividum Hensen, 1988 Chalybion magnum Hensen, 1988 Chalybion malignum (Kohl, 1906) Chalybion sulawesii Ohl & Höhn, 2011 Chalybion tanvinhense Pham, Ohl, & Truong, 2019

Chalybion gredleri species-group Chalybion gredleri (Kohl, 1918) (Democratic Republic of Congo) Chalybion triangulum Hensen, 1988 (Central African Republic, Gambia, Togo)

Chalybion incisum species-group Chalybion incisum Hensen, 1988

Chalybion madecassum species-group Chalybion bonneti Leclercq, 1966 (Madagascar) Chalybion dolichothorax (Kohl, 1918) Chalybion frontale (Kohl, 1906) Chalybion gracile Hensen, 1988 Chalybion iridescens Pham & Ohl, 2025 Chalybion madecassum (Gribodo, 1883) (Madagascar, Seychelles Islands) Chalybion polyphemus Hensen, 1988

Chalybion tibiale species-group Chalybion ammophiloides Hensen, 1988 Chalybion bocandei (Spinola, 1851) Chalybion bocandei bocandei (Spinola, 1851) (Ghana, Guinea, Liberia, Sierre Leone) Chalybion bocandei aeronitens Hensen, 1988 (Central African Republic, Democratic Republic of Congo) Chalybion heinii (Kohl, 1906) Chalybion henseni Schmid-Egger, 2025 Chalybion kenyae Hensen, 1988 (Kenya) Chalybion laevigatum (Kohl, 1888) (Botswana, Ethiopia, Mozambique, Namibia, South Africa, Tanzania, Zanzibar) Chalybion mochii Hensen, 1988 (Kenya) Chalybion parvulum Hensen, 1988 (Kenya) Chalybion planatum (Arnold, 1951) (Ethiopia) Chalybion ruficorne Hensen, 1988 (Central African Republic) Chalybion schulthessirechbergi (Kohl, 1918) (Democratic Republic of Congo) Chalybion sommereni (R.Turner, 1920) (Angola, Kenya, Tanzania, Democratic Republic of Congo) Chalybion tibiale (Fabricius, 1781) (South Africa) Chalybion tomentosum Hensen, 1988

Subgenus Chalybion (Hemichalybion) Kohl, 1918 Chalybion spinolae species-group Chalybion clypeatum (Fairmaire, 1858) (Angola, Cameroon, Ethiopia, Gabon, Mozambique, Tanzania, Democratic Republic of Congo) Chalybion clypeatum clypeatum (Fairmaire, 1858) Chalybion clypeatum lusingi (Leclercq, 1955) (Democratic Republic of Congo) Chalybion clypeatum kiloensis (Leclercq, 1955) (Democratic Republic of Congo) Chalybion spinolae (Lepeletier de Saint Fargeau, 1845) Chalybion spinolae spinolae (Lepeletier, 1845) (Ethiopia, South Africa, Tanzania, Democratic Republic of Congo) Chalybion spinolae rufopictum (Magretti, 1884) (Eritrea, Ethiopia, Mali) Chalybion spinolae saussurei (Kohl, 1918) (South Africa) Chalybion sumatranum (Kohl, 1884)

Chalybion femoratum species-group Chalybion femoratum (Fabricius, 1781)

Extinct species There is one described fossil species of Chalybion: Chalybion mortuum Cockerell, 1907

See also Black-and-yellow mud-dauber wasps (Sceliphron) Organ pipe mud dauber (Trypoxylon politum)

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