Various accounts of cephalopod attacks on humans have been reported since the 13th century. Cephalopods are members of the class Cephalopoda, which include all squid, octopuses, cuttlefish, and nautiluses. Some members of the group are capable of causing injury or even death to humans.
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Tentacles
Tentacles are the major organs used by squid for defending and hunting. They are often confused with arms—octopuses have eight arms, while squid and cuttlefish have eight arms and two tentacles. These tentacles are generally longer than arms and typically have suckers only on their ends instead of along the entire length. The giant squid and colossal squid have some of the largest tentacles in the world, with suckers capable of producing suction forces more than 800 kilopascals (roughly 100 pounds per square inch) and with pointed teeth at the tips.
Beak
The cephalopod beak resembles that of a parrot. It is a tough structure made of chitin and marks the beginning of the cephalopod's digestive system. Colossal squid use their beaks for sharing and slicing prey's flesh to allow the pieces to travel the narrow esophagus.
One of the largest beaks ever recorded was on a 495-kilogram colossal squid. The beak had a lower rostral length of 42.5 millimeters. Many beaks have also been discovered in the stomachs of sperm whales, as the stomach juices dissolve the soft flesh of the squid, leaving the hard beaks behind. The largest beak ever discovered this way had a lower rostral length of 49 millimeters, indicating that the original squid was 600 to 700 kilograms.
Venom
All octopusi have venom, but few are fatally dangerous. The greater blue-ringed octopus, however, is considered to be one of the most venomous animals known; the venom of one is enough to kill ten grown men. It uses the neurotoxin tetrodotoxin, which quickly causes respiratory arrest. Estimates of the number of recorded fatalities caused by blue-ringed octopuses vary, ranging from seven to sixteen deaths; most scholars agree that there are at least eleven.
Octopus attacks
While octopuses generally avoid humans, there have been multiple accounts of attacks. In one such account, a diver was attacked by the octopus he was filming when the octopus attempted to mate with him. When a male octopus "attacks" in an attempt to mate, it uses its suckers to grapple with its target and insert the hectocotylus, the specialized arm housing the sperm packet.
In the 1960s, divers would willingly grapple octopuses in octopus wrestling, a then popular sport in coastal United States. In the annual world championships, held in Puget Sound, Washington, over 100 divers would compete to catch the largest octopus. Some divers would allow the octopus to grab them in an attempt to catch it.
Humboldt squid
Humboldt squid are notorious for their aggression. In Mexico, they are known as diablo rojo (Spanish for 'red devil'): local fishermen's tales claim that people who fell into the waters were devoured within tens of seconds by packs of squid. Wildlife filmmaker Scott Cassell made the documentary "Humboldt: The Man-Eating Squid" for the Dangerous Waters series of the Discovery Channel.
There is some disagreement on the veracity of Humboldt squid aggression. Some scientists claim the only reports of aggression towards humans have occurred when reflective diving gear or flashing lights have been present, acting as provocation. Roger Uzun, a veteran scuba diver and amateur underwater videographer, swam with a swarm of Humboldt squid for approximately 20 minutes, later saying they seemed more curious than aggressive. When not feeding or being hunted, Humboldt squid exhibit curious and intelligent behavior.
Giant squid
In 2003, the crew of a yacht competing to win the round-the-world Jules Verne Trophy reported being attacked by a giant squid several hours after departing from Brittany, France. The squid purportedly latched onto the ship and blocked the rudder with two tentacles. Olivier de Kersauson (captain of the yacht) then stopped the boat, causing the squid to lose interest. "We didn't have anything to scare off this beast, so I don't know what we would have done if it hadn't let go," Kersauson said.