LOOKING at pictures this week of captured Mexican drug gang boss Miguel Angel Trevino Morales I was reminded of the expression "A face only a mother could love".

Even by the scarcely believable standards of nastiness that his fellow Mexican mafiosa colleagues specialise in, Trevino, or Z-40 to give him his Los Zetas cartel codename, was a pretty unpleasant chap.

One of Trevino's favoured methods of dealing with his rivals or those who displeased Los Zetas was El Guiso – the stew.

Let's just say that, depending on the height and weight of the victim, it can take a long time for a body to melt in the flaming diesel of a 55-gallon drum.

Then there were the severed human heads rolled on to a crowded nightclub dancefloor, and the victim whose face was sliced off and stitched to a football before it was dumped with an attached warning note to rival gang members: "Happy New Year, because this will be your last."

It is not surprising the capture of Trevino has led to fevered speculation that the Mexican authorities are at last making inroads in their protracted fight against a cartel that has done more than any other to stain the country's name with its brutality.

So, just how much of a victory is Trevino's capture and what difference if any will it make to the Los Zetas drug operation?

Before addressing these questions it is worth pausing to consider just how much of a problem the cartels, pose as well as the scale of their influence and power.

In a nutshell, Mexico's drug mafias, notably the two biggest, Los Zetas and Sinaloa cartels, have created a violent insurgency the impact and influence of which the likes of al Qaeda or the Taliban could never hope to match.

In all a staggering 70,000 people have died in these narco wars in the past six years, and there is virtually no area of Mexican society untouched by the tentacles of the drug cartels.

Across, the country Los Zetas and Sinaloa now control huge swathes of territory, including large cities such as Ciudad Juarez.

In Mexico they have a saying: "plata o plomo". Translated from Spanish, it means "silver or lead". For someone unlucky enough to be presented with the expression, it usually means they face an unpalatable choice: take a bribe or a bullet.

Not surprisingly as a result of this the cartels have countless politicians, police and judges on their payroll.

In this arena of unbridled corruption and bloodletting, one Mexican cartel has in recent years risen above the rest: Los Zetas.

Today the Zetas command more than 10,000 gunmen from the Rio Grande, on the border with Texas, to deep into central America. According to the US Department of Justice, the Zetas now command the lion's share of an illicit trade in cocaine, methamphetamine and heroin thought to be worth between $18 billion and $39bn annually in North America alone.

Such phenomenal profit is the kind of financial resource many terrorist organisations can only dream of. It also ensures an army of hitmen, assassins and neighbourhood foot soldiers equipped with state-of-the-art technology such as assault rifles, rocket launchers, satellite communications and parts to build improvised submarines able to ferry drugs along coastlines.

In short, the Zetas have more in common with insurgents than traditional gangs, which brings us back to the question of what impact Trevino's capture will have on them.

While there is no denying that Trevino's arrest marks the most significant capture of a Mexican organised crime leader since 2008, it is precisely the Zetas ability to replace its leadership that has made the cartel so successful.

Indeed, Trevino himself only succeeded Heriberto "El Lazca" Lazcano last year after he was killed by the Mexican navy. That succession happened without any noticeable internal strife, a rare occurrence among the Mexican drug cartels.

That they were able to do this stems from the Zetas founding members, several of whom deserted from the highly trained Special Forces Airmobile Group unit of the Mexican army.

Because ex-military personnel formed Los Zetas, members tend to move up in the group's hierarchy through merit rather than through familial connections, a process very different from the culture of other cartels, including Zetas biggest rival the Sinaloa Federation.

That said, Trevino himself did not originate from the Mexican military like his predecessor, leaving intelligence analysts to consider that the Zetas culture may finally have changed.

For now it is likely that Trevino's brother, Omar "Z-42" Trevino, will try to hold the group together.

Should an internal power struggle erupt, however, it will most likely be evident from a corresponding rise in violence across those Mexican states where the Zetas hold sway, notably Tamaulipas, Nuevo Leon, Zacatecas, and San Luis Potosi.

As for Zetas' rivals like the Sinaloa Federation, the Cartel de Jalisco Nueva Generacion, the Knights Templar and factions of the Gulf cartel, they will doubtless do all they can to exploit this moment of weakness.

For his part Mexican President Enrique Pena Nieto will also make great political capital from Trevino's departure from the cartel scene, while the intelligence gleaned from his arrest will be a boon to US drug enforcement agencies.

Pena Nieto has vowed to improve the use of intelligence in the fight. However, as significant a blow as Trevino's arrest is, the president still faces major challenges in his quest to pacify Mexico.

Plata o plomo – silver or lead – looks set to be the rule for some time to come yet.