Humboldt Squid are carnivorous marine invertebrates that move in shoals of up to 1,200 individuals. They swim at speeds of up to 24 kilometres per hour (15 mph/13 kn) propelled by water ejected through a hyponome (siphon) and by two diamond shaped fins. Their tentacles
bear suckers lined with sharp teeth with which they grasp prey and drag it towards a large, sharp beak.
Although Humboldt squid have a reputation of being aggressive, the only reports of aggression towards humans have occurred when reflective diving gear or flashing lights have been present as a provocation. Roger Uzun, a veteran scuba diver and amateur underwater videographer who swam with a swarm of the animals for about 20 minutes, said they seemed to be more curious than aggressive. In reality, there is very likely little danger to humans. In circumstances where these animals are not feeding or being hunted, they exhibit curious and intelligent behavior.
Electronic tagging has shown that Humboldt squid undergo diel vertical migrations which bring them closer to the surface from dusk to dawn. Humboldt Squid are thought to have a lifespan of only about one year, although larger individuals may survive up to two years. They may grow to 1.75 metres (5.7 ft) in mantle length (ML) and weigh up to 50 kilograms (100 lb). They can rapidly change their skin color from deep purplish red to white using chromatophores (specialized skin cells) in what some researchers believe is a complex communication system. Experts have also stated that the squid hunt for their prey of small fish and krill in a cooperative fashion, which would be the first observation of such behavior in invertebrates. Humboldt Squid are known to hunt near the surface at night, taking advantage of the dark to use their keen vision to feed on more plentiful prey.Recent research suggests that Humboldt squid are only aggressive while feeding. At other times, they are quite passive. Their behavior while feeding often extends to cannibalism and they have been seen to readily attack injured or vulnerable squid of their own shoal. This behavior may account for a large proportion of their rapid growth.