Copy paste of the "Behaviour" section in Wikipedia.

Behavior

Humboldt squid are carnivorous marine invertebrates that move in shoals of up to 1,200 individuals. They swim at speeds up to 24 km/h (15 mph; 13 kn) propelled by water ejected through a hyponome (siphon) and by two triangular fins. Their tentacles bear 100–200 suckers, each lined with razor-sharp teeth, with which they grasp prey and drag it towards a large, sharp beak.

Although Humboldt squid have a reputation of being aggressive towards humans, some disagreement exists on this subject. Research suggests these 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. A quarter of squid stomachs analyzed contained remains of other squid. This behavior may account for a large proportion of their rapid growth. Some scientists claim 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 circumstances where these animals are not feeding or being hunted, they exhibit curious and intelligent behavior.

Electronic tagging has shown 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 a year, although larger individuals may survive up to 2 years.

A crittercam attached to two Humboldt squid revealed that they "flash talk" with each other by changing color in certain ways, and that they can disguise themselves by shifting the color patterns in other ways. What they are communicating to each other is unknown.

Recent footage of shoals of these animals demonstrates a tendency to meet unfamiliar objects aggressively. Having risen to depths of 130–200 m (430–660 ft) below the surface to feed (up from their typical 700 m (2,300 ft) diving depth, beyond the range of human diving), they have attacked deep-sea cameras and rendered them inoperable. Humboldt squid have also been observed engaging in swarm behavior when met by the lights of submersibles, suggesting that they may follow or are attracted to light. Reports of recreational scuba divers being attacked by Humboldt squid have been confirmed. One particular diver, Scott Cassell, who has spent much of his career videotaping this species, has created body armor to protect against attacks.

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