The art of hiding in plain sight

At first glance, the focal object in both underwater photographs may appear to be a rock, but look closely: can you see an octopus's eye? And in the left image, a crab's leg hidden between its arms? Having just captured a crab, this common octopus (Octopus vulgaris) now searches for a safe location to enjoy its lunch. But there's a problem: in the immediate vicinity, there are no places to hide. In the blink of an eye, the octopus adopts a spherical shape and changes its skin pattern to mimic nearby benthic objects such as small rocks. Using its ventral arms and bipedal locomotion, the octopus then stealthily leaves the scene (see also https://bit.ly/3XITzTq). Known as the “moving rock” strategy (Biol J Linn Soc 1999; doi.org/10.1111/j.1095-8312.1999.tb01914.x), this innate behavior was initially observed in Octopus cyanea specimens weighing between 300 and 700 g that traversed slowly by “tiptoeing” on their eight arm tips. In O vulgaris, the bipedal version of this behavior is first exhibited in young juveniles weighing less than 1 g, peaks in individuals between 1 and 100 g, and is rarely performed by those above 100 g. The tactic is likely restricted to juveniles because their lighter body mass maintains higher dynamic stability during bipedal locomotion (Science 2005; doi.org/10.1126/science.1109616; Mar Biodivers 2020; doi.org/10.1007/s12526-020-01112-5).