Fluorescence is rare in land animals, being largely limited to parrots and marine turtles. Now, for the first time, it has been found in a frog. Carlos Taboada of CONICET in Buenos Aires and colleagues studied South American polka-dot tree frogs (Hypsiboas punctuatus) collected near Santa Fe in Argentina. The colours of these frogs are normally a combination of muted greens, yellows and reds, but in dim light and UV illumination they glow bright blue and green. This is genuine fluorescence, not the more common bioluminescence in which organisms make their own light. The fluorescent molecules are unlike those in any other animals, being derived from dihydroisoquinoline. In twilight or night-time conditions, the fluorescence contributes 18–29% of the total emerging light, enhancing a creature’s visibility, particularly for amphibians, but the reasons for the fluorescence are still not known.