The Hawaiian bobtail squid (Euprymna scolopes) spends its days buried in sand and its nights stalking prey in the shallow waters off the coast of Hawaii. Just because the squid hunts at night, however, doesn’t mean that it relies on the cover of darkness. Its strategy is quite the opposite, in fact. This tiny speckled squid (an adult is about the size of your thumb) can cruise above its prey without casting a shadow—even on a moonlight night—thanks to its relationship with a bacterial partner, Vibrio fischeri. Juvenile bobtail squid are born without the bacteria; they recruit V. fischeri from the surrounding ocean water and then house the hitchhikers in a specialized light organ. In exchange for room and board, the bacteria help the squid hide at night—by glowing. The light they emit blots out the squid’s shadow, letting it sneak up on prey, and hide from predators.

Directed by Flora Lichtman for bioGraphic: The Glowing Squid, one in a series on Invisible Nature. Related reading: Counter illumination.

Previously: Code of the Treehopper. Plus, more bioluminescence, more paper craft, more videos about all kinds of squids, and this: Symbiosis and a surprising tale of species cooperation.

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