Some years ago, while doing research on angelfish on the Papuan Barrier Reef, I was lying on a white sandy bottom 30 meters down observing males competing for females during the sunset spawning time.
After a lengthy period of motionless observation, I moved my right leg and it bumped into what I took to be a sand-covered rock. Only then did a formerly motionless stonefish emerge from the sand, spines fully erected in threatening mode -- spines so toxic they are often lethal to humans.
I instantly backed away; however, the vast majority of the reef fishes rushed at the stonefish from all sides. Included in the initial attack were damselfish, basslets, butterfly fish and a single pygmy angelfish that lunged at the stonefish with repeated biting attacks. All these attackers are either loosely or strongly territorial species.
However, their unusual behavior quickly attracted larger, nonterritorial foragers and hunters, including parrotfish, an immense jack and a single grey reef shark.
The stonefish soon retreated away from the reef.
What I'd witnessed was a fairly common type of animal behavior known as "mobbing." Other examples include baboons mobbing lions on the African plains. Closer to home, you may have seen sparrows, bulbuls, Japanese magpies and other species get excited and make swooping, shrieking mock attacks on cats.
When I ran my ocean schools at Miyakejima before the ongoing volcanic eruptions began, large long-legged house spiders lived in relative abundance in my 100-year-old farmhouse, dining on all manner of insects they caught. Invariably, the sight of one of these ferocious-looking creatures triggered mobbing behavior by nearly every participant in the school, and even some staff members.
Sadly, their most common aim was to kill the "intruder" -- though when I could, I always protected them and got the mobbers to subdue their aggression on the basis that the spiders were both harmless and beneficial.
Mobbing has what scientists refer to as "survival value." The animals mobbed are perceived as dangerous, and in many cases -- such as with the stonefish and lions -- they truly represent a threat. However, mobbing is not caused entirely by direct experience, but results, at least in part, from an evolutionary DNA message warning countless species to beware of certain others.
In the case of the spider-mobbing, the humans' attacks resulted from "mistaken identity," because those spiders posed no threat to them. However, the DNA message that prompted the mobbing does have survival value, because some species are dangerous.
It is worth noting that species that exhibit the most mobbing tendencies are strongly territorial, like the Japanese magpie and damselfish.
It is interesting, too, that we humans are fiercely territorial, and that this characteristic of individuals could be said to show up collectively in nationalism. Because most humans presently live in nation states, not all of which are friendly, nationalism does, in that sense, have survival value.
However, it can also be also be dangerous -- especially when a people begin to believe their nation is superior to all others, and is entitled to take unilateral, "mobbing" military action against whatever or whoever they perceive to be threatening.