Halobates is exposed to continuous insolation at the sea surface throughout its life. Although the UV-absorbance spectrum of its dorsal cuticle (260-450 nm) is similar to those of related species from inshore and freshwater habitats where shelter from sunlight is available, the UV absorbance of the cuticle in a direction perpendicular to its outer surface is much higher in Halobates than in a mangrove-dwelling Rheumatobates or a stream-dwelling Gerris.