New Zealand is said to have more gang members than soldiers.
More than 5300 members or "prospects" are lining up to join one of 25 listed groups.
A recent article by The Economist quoted police saying gangs were a bigger force than the army, and organised criminal groups were thriving in rural areas as well as cities.
The Hell's Angels, Head Hunters, Nomads and Killer Beez all have a presence in New Zealand. Black Power and the Mongrel Mob have ruled the roost for almost half a century.
Gang members "stick out like dogs' balls", one member admitted to The Economist, because of their patches and tattoos. They are often clothed in leather jackets branded with clenched fists, bulldogs or the Nazi salute.
Police say three-quarters of the country's mobsters are Maori - despite the fact they make up just 15 per cent of the population.
Many said they joined as much for whanau, as for money, power or thrills, The Economist said.
"People have this idea we are all rapists and murderers and methamphetamine cooks. But not all gang members are criminals," lamented Eugene Ryder, a leader of Black Power in Wellington, who requires his underlings to study or take full-time jobs.
For decades the groups have fought ruthlessly for turf, beat and raped women, and pushed wannabe members into violent crime to earn their stripes, but The Economist reports times are changing and ageing leaders are now prohibiting gang rapes and campaigning against methamphetamine use.
Mane Adams, a Black Power boss, began campaigning against the drug after a comrade disembowelled himself in meth-induced psychosis. Leaders are also said to now criticise, rather than joke about, domestic violence, and street battles have grown less frequent.
Neil Campbell, who heads the Maori division of the Corrections Department, told The Economist some "pro-social" gang members really "do want better for their children".
But despite a move towards reform, about a third of inmates are gang members and gangs account for more than 14 per cent of all murder charges, according to police.
The Economist reports locking gang members up has arguably exacerbated the problem, by turning jails into recruitment grounds.
Adams said "nine times out of ten" inmates will "turn to a gang just for protection", and some leaders have taken to tattooing the faces of prison recruits, to guarantee fealty when they are free.
The rise of new, more destructive rivals and teenage outfits has also created a new forum for unpredictable and violent crime.
* A version of this article appeared in the Asia section of The Economist print edition under the headline "Bigger than the army".