These wasp nests give off one of the most powerful green glows in the animal kingdom

© Bernd Schöllhorn and Serge Berthier

One of the brightest green glows in the animal kingdom doesn’t come from a firefly or a deep-sea fish—it radiates from the nests of the Asian paper wasp, according to a new study.

The light (pictured) appears to derive from silk proteins woven into cocoons by the wasp larvae (genus Polistes). With just a hand-held ultraviolet (UV) lamp, it can be seen up to 20 meters away, researchers report today in the Journal of the Royal Society Interface.

The glow may serve as a homing signal to help the diurnal wasps find their way back to the nest at dawn and dusk—a time when there’s a bit of UV light from the Sun, but the environment is still mostly dark. Like most animals, Polistes have vision that is optimized to view certain wavelengths of light, and one such peak comes at 540 nanometers, which happens to correspond to the green glow given off by the cocoons.

Another possibility is that the fluorescent proteins protect the developing larvae by absorbing the Sun’s harmful UV radiation and thus blocking it from entering the cocoon. The fluorescence could also be useful for helping the larvae grow: The researchers point out that many Polistes species develop during the rainy season in the jungle when it’s often foggy or cloudy. The extra green light, they say, could be used to reinforce the day-night cycle, which may be crucial for proper development—a sort of cocoon sunlamp for dreary jungle days.