Squids communicate in the pitch-black depths of the ocean with displays of speckled light.

Benjamin Burford at Stanford University in Pacific Grove, California, and Bruce Robison at the Monterey Bay Aquarium Research Institute in Moss Landing, California, analysed hours of footage of roving groups of gregarious Humboldt squid (Dosidicus gigas), captured by a camera mounted on a remotely operated vehicle navigating off California’s coast. In the ocean’s dark reaches, these squid 'flashed' or 'flickered' when in the presence of others of their kind. To do so, the animals turned on internal bioluminescent organs that made their entire bodies glow — except where the glow was covered by overlying patterns of pigmentation.

But when squids pursued prey, they dimmed themselves. Then, just before striking, they suddenly flashed a splotchy pattern by lighting up organs beneath intermittently pigmented parts of their body.

The authors suggest that the displays help individual squid to avoid bumping into one another while swimming together, and might allow them to cooperate rather than compete for prey.