An Octopus Used a Mirror to Hunt

A crab is hidden around a corner. The octopus can't see it directly, but it can see the crab's reflection in a mirror. After 10 to 12 tries, it stops detouring to the glass and heads straight for dinner.

Researchers at Dartmouth decided to test not self-recognition, but something one step back: whether octopuses can use mirrors as a tool at all. The classic mirror test, the one that puts a dot between an animal's eyes and watches to see if it investigates its own reflection, runs into a problem with octopuses. Their skin is covered in specialized sensory cells, so there's no guarantee the animal wouldn't just feel the mark rather than notice it visually. Underwater marking logistics don't help either. The study is the first to document this kind of mirror-guided behavior in an invertebrate.

Then came the real test. Each octopus sat in a small box facing a large mirror. A screen on the wall behind it showed a virtual crab, visible only in the reflection. The crab was virtual on purpose, since octopuses can smell and taste through touch. To win a real crab, the octopus had to leave the box, turn around and head for the side the mirror had shown. Over dozens of trials, the octopuses got it right about 70 percent of the time, more often than chance could explain.

Some went further. Instead of walking around, they climbed straight up and over the box's wall, a shortcut that showed up in 59 percent of correct trials. One octopus did it on its very first try.

The two-spot octopus gets its name from a pair of false eyes on its skin. As it turns out, the real eyes were paying close attention.

Read the full story at Popular Science, September 29, 2026

Hot Take: We use mirrors to check our teeth for spinach. Octopuses use mirrors to find dinner.