Octopus punches fish in the head —just because it can

Why do octopuses have eight arms? The better to punch fish with, new research reveals.These brainy cephalopods sometimes team up with fish to find food; hunting collaboratively like this allows them to cover more area, and it increases their chances of catching prey. However, when big blue octopuses (Octopus cyanea), also known as day octopuses, are displeased with their fish partners, they demonstrate their ire by suddenly punching the fish in the head.The octopus lashes out using "a swift, explosive motion with one arm," in an attack "which we refer to as punching," scientists wrote in a new study.

Temporary hunting alliances between octopuses and coral reef fish have been documented for decades and can involve multiple participants of various species, the study authors reported Dec. 18 in the journal Ecology. Sometimes, fish and octopuses will work together for more than an hour, with different species scouting different locations. Octopuses pursue prey that dart around rocks and into tight spaces in the reef, while bottom-feeding fish such as the yellow-saddle goatfish (Parupeneus cyclostomus) scour the seafloor, and other fish species patrol the water column, according to the study.

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