Crazy Little Squid Hunts by Moonlight, Glows to Hide Its Shadow

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Bobtail Squid

credit: Mark R. Smith/bioGraphic

To prevent potential prey from spotting its shadow on the seafloor, the bobtail squid emits just enough light to match the moonlight shining upon it. The absolute wonder and brilliance of Mother Nature can be seen in creatures great and small; in the case of the Hawaiian bobtail squid (Euprymna scolopes), we're talking a mere inch in length. The bite-size hunters who inhabit the shallow waters off of the Hawaiian Islands stay out of sight by day, burying their little selves in the sand. But once nighttime comes, they do something extraordinary. Hunting for shrimp by the light of the moon and the stars, the squid begins to emit a glow. While at first it might seem counterintuitive for the wee creatures to call attention to themselves by glowing, they're actually a step ahead of us. They are deploying a tactic called counter-illumination – they emit just enough light to match the moonlight from above, effectively erasing their shadows from the seafloor so that predators can't stalk them by the dark shape below. Even more remarkable is that the squid get their glow courtesy of a rare bioluminescent bacteria, Vibrio fischeri, that the they fill up their light organs with. Using its ink sac as a shutter, bioGraphic explains, the squid can stem the flow of light depending on the fullness of the moon and the cloud cover in the sky. Every morning when it's time to hit the hay, or the sand as the case me be, the squid flush out the remaining V. fischeri and get a new batch during the course of the day. The image above was taken by award-winning science photographer Mark R. Smith, who is helping molecular and cell biologists at the University of Connecticut discover how the squid’s immune system can recognize V. fischeri and grant it exclusive entrance into the light organ. Smith uses a technique called focus stacking, in which multiple photos at different focal lengths are digitally combined to create high-res photos of unprecedented color, depth, and detail. The scientists are are hoping to eventually learn more about our own relationship to bacteria ... and in the meantime, the rest of us get extraordinary images of a tiny squid who has mastered the art of optical illusion.