An animal armed with another animal
In the open waters of the Great Barrier Reef, the blanket octopus (Tremoctopus) employs a defense mechanism unknown to almost any other creature. It actively seeks out, attacks, and dismembers one of the most venomous creatures in the ocean: the Portuguese man o' war (Physalia physalis). The blanket octopus is completely immune to the man o' war's powerful venom. Young female and male blanket octopuses will rip the stinging tentacles from a living man o' war and wield them like whips for both defense and hunting.
The man o' war is not a true jellyfish but a siphonophore, a colony of individual organisms called zooids. Its tentacles, which can reach lengths of 10 meters, are covered in nematocysts—microscopic and spring-loaded barbs that inject a potent neurotoxin. This venom can paralyze and kill small fish and cause excruciating pain in humans. Detached tentacles remain venomous for hours or even days. The octopus carefully uses its suckers to carry these toxic weapons, effectively extending its reach and providing a shocking deterrent to would-be predators. This behavior shows tool use among invertebrates, first documented in 1963. Scientists theorize the immunity may stem from specialized skin chemistry that prevents the nematocysts from firing, combined with a physiological resistance to the venom itself.