Ultraviolet (UV) wavelengths invisible to humans are primarily studied in the context of reproduction and social signaling. This narrow focus can arise from bias in taxa studied, which are often brightly colored in human-visible wavelengths. Our research describes undocumented UV color patterns across 110 diverse species of Western Hemisphere snakes and tests the hypothesized roles of reproduction versus predator avoidance in the evolution of UV coloration. Phylogenetically-informed tests of life stage, sex, and habitat showed unexpected support for the predator defense hypothesis, with pronounced differences in snake conspicuousness explained by UV coloration. UV reflectance was not predictable from any aspect of visible color pattern, suggesting high potential for transformative discoveries in other “cryptically-colored” lineages across the tree of life.
