Photo: a giant squid with glowing arms
This giant squid's unusual weapon—glowing arms—can blind and stun prey.

Photograph courtesy Royal Society

Monster-size squid that glow in the dark have been filmed for the first time in the wild. The creatures were videotaped in the inky depths of the North Pacific Ocean off southeastern Japan. The new footage shows the squid, which can grow as big as humans, using bright, flashing lights on their arms to dazzle and catch prey.

The discovery was made by Japanese scientists who lured the massive squid with bait that was lowered alongside cameras deep down in the ocean from a research ship.

Known as the Dana octopus squid, or Taningia danae, this eight-armed species has catlike claws on its suckers but lacks the two long feeding tentacles that other big squid use to grab prey. Instead, scientists think, the deep-sea squid traps its victims using light-producing organs on the ends of two of its arms, stunning them with blinding flashes.

These organs, about the size of lemons, are called photophores. They are the largest photophores found in the animal kingdom and can be opened and closed like eyes.

The squid were filmed at depths of 780 to 3,100 feet (240 to 940 meters) during an expedition led by Tsunemi Kubodera of the National Science Museum in Tokyo, Japan. Kubodera’s team also captured
the first-ever images of a live giant squid, also known as Architeuthis, in 2004.

The team says the Dana octopus squid also glowed when it wasn’t hunting. The researchers think these glows are used for communication, such as to warn other squid of danger or for attracting a mate. 

Experts say the new video footage backs up what scientists previously thought about the way this glowing squid behaves.

“It’s nice to have some evidence,” says squid researcher Michael Vecchione of the Smithsonian’s National Museum of Natural History. “Mostly it’s been speculation up until now."

The footage also shows the Dana octopus squid is a powerful and agile hunter.

“Some people have said all deepwater squid are pretty sluggish because their muscles are not real firm when you catch them,” says Vecchione. “But this particular family has got very muscular fins, and that’s what it’s using for swimming.”

The squid is thought to be one of the world’s five biggest squid. The largest recorded specimen was caught in fishing nets off the coast of Maine in the United States in 1993. It weighed 135 pounds (61 kilograms) and measured 7.6 feet (2.3 meters) long. But living adults had never been seen until now.

The Japanese researchers followed sperm whales to track down the mysterious creatures because these whales love to eat big squid. Dead sperm whales have been found with hundreds of hard squid beaks inside their stomachs. Whales obviously find monster glowing squid a lot less scary than most humans do!