Octopuses, it turns out, know what they're looking at when they look in a mirror — or at least enough to use the reflection to their advantage. A study published in the journal Current Biology found that California two-spot octopuses (Octopus bimaculoides) learned to use a mirror to locate food hidden outside their direct line of sight — the first time this kind of mirror-guided foraging has been documented in an invertebrate.
The research was led by Mary Kieseler, who ran the study as a doctoral student at Dartmouth College and is now a postdoctoral researcher at the University of Fribourg in Switzerland. In the experiments, three octopuses were trained to associate a mirror's reflection with the true location of a reward placed around a corner or behind a barrier. All three learned the task, choosing the correct side roughly 70 percent of the time across repeated trials — well above chance.
Some of the octopuses went further than simply following instructions, finding shortcuts to the reward rather than mechanically repeating the exact path they had been trained on, a sign the animals were building some kind of spatial map rather than memorizing a single route.
"This represents convergent evolution — unrelated species independently developing similar cognitive abilities."
— Mary Kieseler, University of Fribourg
Mirror-guided problem-solving has previously been documented mainly in vertebrates — some primates, dolphins, elephants and a handful of bird species — making octopuses, which diverged from the vertebrate lineage more than 500 million years ago, a striking addition to that list. Researchers say the octopus's innate three-dimensional spatial awareness, evolved for hunting prey and evading predators in complex reef environments, likely gave it the raw cognitive tools to interpret a reflection as useful information rather than a confusing illusion.
The finding adds to a fast-growing body of octopus research — on arm coordination, tool use and problem-solving — that has made the soft-bodied, famously short-lived animals a go-to case study for scientists probing how intelligence can evolve along entirely different paths than it did in humans.