The bat wing is a highly adaptive airfoil that enables demanding flight maneuvers that are performed with robustness under turbulent conditions, and stability at slow flight speeds. The bat wing is covered with microscopically small, tactile hairs that have been shown to be involved in sensing air flow for improved flight maneuverability in 2 bat species, the frugivorous–nectarivorous Carollia perspicillata and the insectivorous Eptesicus fuscus. Here, we provide comparative data on the anatomy of these hairs and their distribution on the wing surface in 4 species of bats (C. perspicillata, Desmodus rotundus, E. fuscus, and Rousettus aegyptiacus), based on scanning electron microscopy analyses. Hairs were found on both the dorsal and ventral surfaces of the wing in all species, including the bony structures. They were generally sparsely distributed (1–3 hairs/mm2) and often found arranged in single file along elastin bands that extend through the wing membrane. Fringes of hairs also were found at the leading edge of the propatagium. The hairs were strongly tapered in all species. Their length varied from 0.08 mm (E. fuscus) to 3 mm (R. aegyptiacus). Hair length correlated positively with the body mass and wing loading value of each species, but not with aspect ratio, flight speed, or diet. We conclude that the hairs are spaced so that viscous coupling is negligible, at least for single-file hairs, and that they are scaled to the boundary layer of airflow limited to the first few millimeters close to the wing surface.