Summary: A new study provided the first empirical evidence that invertebrates can utilize mirrors as an abstract spatial tool to interpret their surrounding environment. The study demonstrates that the California two-spot octopus (Octopus bimaculoides) can process mirror reflections to locate and intercept prey hidden completely out of their direct line of sight.
By proving that an organism so evolutionarily distant from humans can master this visual task, the research suggests that complex spatial cognition may be a product of convergent evolution, where distinct species independently evolve identical neural solutions to ecological challenges.
Key Facts
- The Invertebrate Cognitive First: While mirror utility has been documented in highly intelligent vertebrates like certain mammals and birds, this study represents the first time an invertebrate has demonstrated the ability to use mirrors to decode spatial environments.
- The 73% Intercept Accuracy: Training trials conducted in the Octopus Lab at Dartmouth revealed that octopuses successfully utilized mirror reflections to navigate to the correct hidden location approximately 73% of the time.
- The Virtual Prey Protocol: Because octopuses possess advanced chemoreceptors that allow them to smell and taste by touch, researchers swapped out live crabs for a projected virtual crab stimulus to ensure the animals were relying strictly on visual inference rather than olfactory or tactile cues.
- The 180-Degree Navigation Maneuver: Placed inside a start box facing a mirror, the octopuses observed a virtual crab projected from behind them. Instead of attacking the mirror image, the animals made a full 180-degree turn or climbed over the enclosure walls to strike the actual projection site for a live food reward.
- Spatial Mapping Acceleration: Overhead tracking of a spot between the eyes on the octopus’s mantle showed that while the animals did not always chart the absolute shortest physical path of travel, they became progressively faster at calculating and reaching the hidden stimulus site.
- Convergent Evolution Evidence: Lead author Mary Kieseler notes that because humans and octopuses split from a common worm-like ancestor 350 to 500 million years ago, this independent development of spatial processing indicates that complex cognitive solutions evolve symmetrically across disparate branches of life.
- The Internal Map Hypothesis: Senior author Peter Tse suggests that this ability to infer real-world coordinates from a reflection indicates that octopuses likely possess sophisticated internal representations of space and mental territory maps to hunt efficiently in complex coral reefs.
Source: Dartmouth College
Octopuses are remarkably intelligent creatures, as was demonstrated by Inky the Octopus’s famous escape from the National Aquarium of New Zealand through a drainpipe back to sea in 2016.
A new Dartmouth study shows octopuses can use mirrors to find food out of sight, demonstrating spatial cognitive abilities.
The results are published in Current Biology.
“Our findings are the first to demonstrate that invertebrates can use mirrors to understand their environment to find prey,” says lead author Mary Kieseler, Guarini ’25, who conducted the research as a PhD student in the Department of Psychological and Brain Sciences at Dartmouth and is now a postdoc at Switzerland’s University of Fribourg. “It’s a skill that previously has only been documented in vertebrates, such as in some mammals and some birds.”
The researchers trained three California two-spot octopuses (Octopus bimaculoides) in the Octopus Lab at Dartmouth to not attack a crab image that they see in a mirror but instead to infer and move to where the hidden stimulus was displayed behind them.
First, the octopuses were acclimated to the mirror in their habitat. Then, they were trained to understand how a mirror works using a live food reward—crab—which was placed in a glass jar that they could see in the mirror. To obtain the crab, the octopus had to make a 90-degree turn around a corner.
“We don’t enter the world knowing how to use a mirror but learn how to use a mirror,” says senior author and cognitive neuroscientist Peter Tse, a professor of psychological and brain sciences at Dartmouth. Just as new drivers learn to use a rearview mirror to track other vehicles, “Octopuses can also learn how to use a mirror to infer where things are in the world.”
Octopuses have chemoreceptors that enable them to smell and taste by touch. So, for the experiment, the team used a virtual crab stimulus rather than a live crab.
The octopus was placed in a start box open to the top and front and shown the virtual crab image in a mirror directly in front of the animal. The virtual crab image was projected from behind the octopus on the left or right side. Instead of the octopus going to the mirror to try and obtain the virtual crab, it went to the projection site, requiring a 180-degree turn, where it then received a live crab reward. In some cases, the octopus would climb up and over the box to the side where the crab was projected rather than exiting the box and swimming around to the side.
The results show that octopuses travelled to the correct side approximately 73% of the time.
During the trials, the team manually tracked a spot between the eyes on the mantle, which is like the head of the octopus, from overhead. The researchers also calculated the length of the paths the octopuses used to seek the reward. While they did not always choose the shortest way of travel, they became faster at going to where the stimulus was based.
“Octopuses are among the most evolutionarily distant animals from humans, as our last common ancestor was a worm that lived 350 to 500 million years ago,” says Kieseler. “Given that such a remote organism has independently evolved the means to use a mirror as a tool to process spatial cognition suggests that the underlying cognitive processes might be subject to convergent evolution, where different species evolve similar neural solutions to the same challenge.”
The world in which octopuses live, mainly coral reefs and the ocean seafloor, are complex environments.
“Octopuses are like cats: they will sneak up on their prey and pounce, and they want to do so as fast as possible, so that they don’t become preyed upon,” Tse says.
“Hunters are very effective when they have a mental map of their territory, so that they know where they are in relation to their environments,” says Tse. “Our work suggests that octopuses might also have internal maps, an internal representation of space.”
However, according to the co-authors, additional research is needed to prove this.
Key Questions Answered:
A: To ensure the octopuses were using their brains to read the mirror rather than their chemical senses. Because octopuses have powerful chemoreceptors on their skin that allow them to smell and taste through basic touch, using a projected digital image forced the animals to rely entirely on visual logic and spatial inference to find the food.
A: Because instead of swimming straight ahead to attack the reflection in the glass, the octopus calculated where the prey was actually hiding. It observed the reflection in front of it, inferred that the real target was located behind its body, and executed a complete 180-degree turn, or climbed over the back of its enclosure, to strike the hidden zone.
A: It points directly to a process called convergent evolution. Humans and octopuses are separated by hundreds of millions of years of evolution, yet both have independently developed the exact same cognitive ability to use mirrors as spatial tools, showing that completely different species can evolve identical neural solutions to survive in complex environments.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this neuroscience research news
Author: Amy Olson
Source: Dartmouth College
Contact: Amy Olson – Dartmouth College
Image: The image is credited to Mary Kieseler
Original Research: Closed access.
“Octopus bimaculoides can learn to utilize a mirror to localize a reward outside the line of sight” by Mary Kieseler, Marvin R. Maechler, Kelly R. Finn, Carl Harris, Jay Michael Vincelli, Zachary Hoffman, Navneet Dhanoa, Jean Fang, Scott Gies, James McHugh, III, Julia Valenti, Mira Ram, John O. Fitzgerald, Madison Augusto, David Edelman, and Peter U. Tse. Current Biology
DOI:10.1016/j.cub.2026.05.012
Abstract
Octopus bimaculoides can learn to utilize a mirror to localize a reward outside the line of sight
Mirror-mediated localization of hidden objects is well documented in vertebrates but has never been demonstrated in invertebrates. Using mirrors to locate otherwise occluded objects is a form of mediated perception, linking a visible reflection to an occluded location and is seen by some as a precursor to self-recognition.
Cephalopods offer a fascinating test case of convergent cognition, having independently evolved sophisticated perceptual and cognitive abilities that are similar to mammals, after diverging from a common ancestor over 520 million years ago.
In addition, they react to mirror images as though they were conspecifics. We projected a virtual crab that was visible only via mirror reflection onto a tank wall. Three Octopus bimaculoides were trained to navigate to the projection site instead of the mirror.
All three octopuses learned this task, successfully choosing the correct side in 73% of trials. Critically, octopuses sometimes moved away from the visible reflection and climbed over the side walls of the start chamber to reach visually occluded locations that were spatially aligned with the reflected prey location. This behavior suggests (1) the ability to inhibit a direct approach to salient visual stimuli, and (2) a spatial representation that integrates mirror information with knowledge of 3D tank geometry.
These findings extend mirror-use capabilities to invertebrates, demonstrating that cephalopods can employ mirror reflections for spatial navigation. The independent evolution of cognitive capacities underlying mirror use across diverse taxa suggests that common solutions may have evolved to solve spatial navigation challenges.
