Octopuses have long been famous for their remarkable intelligence. One well-known example is Inky, the octopus that escaped from New Zealand’s National Aquarium in 2016 by slipping out of its tank, squeezing through a drainpipe, and making its way back to the ocean.
Now, researchers at Dartmouth have identified another impressive ability. A new study published in Current Biology suggests that octopuses can learn to use mirrors to find food hidden from direct view, revealing a sophisticated form of spatial thinking.
According to lead author Mary Kieseler, this is the first evidence that invertebrates can use mirrors to interpret their surroundings and locate prey. Until now, this skill had only been documented in vertebrates, including some mammals and birds.
Teaching Octopuses to Use Mirrors
The study involved three California two-spot octopuses (Octopus bimaculoides) housed in Dartmouth’s Octopus Lab.
The researchers wanted to find out whether the animals could learn to use a mirror to determine the position of food they could not see directly. The key question was whether the octopuses would merely react to a reflection or understand where the object was actually located and move toward that place.
First, the octopuses were given time to become familiar with a mirror placed in their habitat. Then the researchers trained them to connect what they saw in the reflection with the real position of objects in the environment. During this stage, a live crab was placed inside a glass jar so that the octopus could see it only in the mirror. To reach the crab, the animal had to turn 90 degrees and move around a corner.
Senior author Peter Tse, a cognitive neuroscientist at Dartmouth, noted that humans are not born knowing how to use mirrors either — they learn. New drivers, for example, gradually learn how to use a rearview mirror to track cars behind them. In a similar way, the researchers argue, octopuses can learn to use mirrors to infer where things are in space.
Testing Spatial Thinking
Octopuses have chemoreceptors that allow them to “smell” and “taste” through touch. Because real prey might have introduced scent or other cues during the final tests, the researchers used a virtual crab image instead.
In the experiment, each octopus was placed in a start box that was open at the front and top. A mirror stood directly in front of the animal. The virtual crab appeared behind the octopus, either on the left or right side, but it could be seen only in the mirror.
To receive a reward, the octopus had to understand where the image was actually located and move toward that position. Instead of approaching the mirror, the animals turned around and went to the correct side, where they were given a live crab. Some even climbed over the side of the box to reach the projected image’s location more directly rather than swimming around.
Overall, the octopuses chose the correct side about 73% of the time.
The researchers also tracked the animals’ movements from above, following a point between the eyes on the mantle, the body region roughly comparable to a head. They analyzed the routes the octopuses took while seeking the reward. Although the animals did not always choose the shortest path, they became faster at reaching the correct location as the trials continued.
What This Reveals About the Evolution of Intelligence
The findings may help scientists better understand how intelligence evolves across different branches of life.
Octopuses are evolutionarily very distant from humans. Our last common ancestor was a worm-like creature that lived roughly 350 million to 500 million years ago. The fact that such a distant organism appears to have independently evolved the ability to use mirrors as a tool for spatial reasoning may point to convergent evolution: different species arriving at similar cognitive solutions when faced with similar challenges.
The environments where octopuses live — coral reefs, seafloors, and other complex underwater landscapes — are full of obstacles, hiding places, and threats. Navigating such surroundings may require a strong sense of spatial awareness.
Tse compares octopuses to cats: they sneak up on prey, strike quickly, and try to avoid becoming prey themselves. This kind of hunting strategy may benefit from an internal understanding of the surrounding environment.
The researchers suggest that octopuses may possess an internal representation of space — something like a mental map. However, they emphasize that more research is needed before scientists can confirm whether octopuses truly maintain such maps.
Even so, the study adds another remarkable ability to the growing list of traits that make octopuses some of the most fascinating and intelligent animals in the ocean.