Researchers reported on June 3 in Current Biology that the California two-spot octopus (Octopus bimaculoides) can learn to use mirrors. The study indicated that these octopuses are capable of using reflections to locate hidden prey.

Neuroscientist Mary Kieseler, from the University of Fribourg in Switzerland, and her team habituated three wild-caught octopuses to a mirror covering half of their tank. The research involved placing a hidden jar containing a crab, positioned so that the prey could be found only by using its reflection in the mirror. Each octopus completed approximately one trial per day.

After about 10 to 12 trials, each octopus learned to crawl directly to the crab without first approaching the mirror. Kieseler noted, "They did plenty of trials where they just fell asleep or sat in front of the mirror."

In a separate experiment, each octopus was placed in a small three-sided chamber, which blocked their view of anything except a mirror at the tank's front. A screen behind the chamber displayed videos of a crab appearing to move along either side of the back wall, creating a reflection visible to the octopus. The octopuses had to navigate out of the chamber and move to the correct side to receive a real crab as a reward.

The octopuses successfully chose the correct side in about 73 percent of the trials involving virtual crabs. In 59 percent of their correct trials, the octopuses climbed over the side walls of the chamber to reach the crab stimulus, rather than approaching the mirror. Trevor Wardill, a neurobiologist at the University of Minnesota in Minneapolis who was not involved in the research, commented on these findings. Wardill said, "This shows that octopuses can understand how a mirror represents the location of an object, rather than just going impulsively to the mirror reflection hoping to get a reward."