Male fringe-lipped bats wear an odorous crust on their cuffs, perhaps to signal readiness to mate.
Researchers noticed the build-up on the forearms of males of the species (Trachops cirrhosus); females’ forearms, however, remained clean. Males with forearm crusts also displayed enlarged testes, which further suggests the crust is a reproductive trait specific to males. Victoria Flores at the University of Chicago in Illinois and Rachel Page at the Smithsonian Tropical Research Institute in Panama observed male bats rubbing the scent along their arms. The smelly cocktail might be a signal to females or a deterrent to rival males.
The exact chemical make-up of the forearm crust is a mystery. The bats themselves do not seem to secrete the crust material, which is probably concocted from external ingredients.