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.
Extreme biological differences
The blanket octopus has the most extreme size difference between sexes of any large animal. Females can grow up to 2 meters (6.6 feet) in length, while males reach a mere 2.4 centimeters (about 1 inch). This gives them a weight ratio that can be as high as 40,000:1. The female's common name comes from the long, fleshy webbing that connects her dorsal arms. When threatened, she can unfurl this "blanket" to dramatically increase her apparent size and intimidate predators. She can also shed this webbing as a distraction, much like a lizard detaching its tail.
Reproduction for the blanket octopus is a terminal event for the male. He possesses a specialized arm called a hectocotylus, which is filled with sperm. Upon finding a suitable female, he detaches this entire arm and gives it to her. The female stores the arm in her mantle cavity until she is ready to fertilize her eggs. The male dies shortly after this encounter. Females will carry their clutch of up to 100,000 eggs until they hatch.