title: Snake velvet black: hierarchical micro- and nanostructure enhances dark colouration in Bitis rhinoceros.
abstract: The West African Gaboon viper (Bitis rhinoceros) is a master of camouflage due to its colouration pattern. Its skin is geometrically patterned and features black spots that purport an exceptional spatial depth due to their velvety surface texture. Our study shades light on micromorphology, optical characteristics and principles behind such a velvet black appearance. We revealed a unique hierarchical pattern of leaf-like microstructures striated with nanoridges on the snake scales that coincides with the distribution of black colouration. Velvet black sites demonstrate four times lower reflectance and higher absorbance than other scales in the UV-near IR spectral range. The combination of surface structures impeding reflectance and absorbing dark pigments, deposited in the skin material, provides reflecting less than 11% of the light reflected by a polytetrafluoroethylene diffuse reflectance standard in any direction. A view-angle independent black structural colour in snakes is reported here for the first time.
authors.affiliation: Functional Morphology and Biomechanics, Zoological Institute, Kiel University, Am Botanischen Garten 1-9, 24118 Kiel, Germany. spinner@unibonn.de
authors.forename: Marlene
authors.initials: M
authors.lastname: Spinner
authors.forename: Alexander
authors.initials: A
authors.lastname: Kovalev
authors.forename: Stanislav N
authors.initials: SN
authors.lastname: Gorb
authors.forename: Guido
authors.initials: G
authors.lastname: Westhoff
mesh_terms: D000818:Animals; D012867:Skin / Q000033:anatomy & histology* / Q000166:cytology / Q000648:ultrastructure; D012880:Skin Pigmentation; D013057:Spectrum Analysis; D017819:Viperidae / Q000033:anatomy & histology*