The Japanese pinecone fish searches for food with living headlights. This ­­hand-sized fish harbours colonies of light-producing bacteria in two organs on its lower jaw. The beams from these organs shine forward, and when night falls and the fish goes searching for food, its jaw-lamps light the way.

Elsewhere in the Pacific Ocean, the Hawaiian bobtail squid also uses luminous bacteria, but theirs act as a cloaking device. They produce a dim glow that matches the strength of moonlight from above, hiding the squid’s silhouette from hungry fish below. It’s a mutual relationship; the squid gets protection and it pays its residents with sugars and amino acids.

The glowing bacteria of these two animals may have different uses, but