This week it was an 80cm boa constrictor curled up in a shipping container of ornamental palms from Guatemala, discovered by Auckland port workers.

In July a 19-year-old man was jailed for smuggling in two brown and cream mottled corn snakes from Bangkok in his pants.

And, in May 2008, the stowaway was a 55cm ground boa from Indonesia or Papua New Guinea which made its way to Tauranga underneath an empty shipping container from Vanuatu.

The Ministry of Agriculture and Forestry says it is no longer unusual for live snakes to make it to New Zealand. Quarantine inspectors from around New Zealand are being sent each year to a snake catcher's course in Adelaide, South Australia, as the frequency of such discoveries increases.

Inspectors are equipped with snake hooks, tongs, gloves, goggles, catch bags and first-aid gear. Detector dogs trained to scent reptiles are available if required. When discovered the snakes are put down immediately.

The ministry seems nervous about these incursions and perhaps with good cause. New Zealand already provides a damp, temperate climate conducive to snakes.

"Snakes are excluded by law from entering New Zealand. There are no exceptions which is why they are not found in zoos, research establishments or accompanying visiting entertainers," says Jaimie Baird, a quarantine inspector in Nelson and one of 24 Biosecurity New Zealand staff trained to deal with serpent trespassers.

Smugglers face hefty penalties: a maximum of five years in jail and fines of up to $100,000.

Mike Mullany, who was 18 when he smuggled in the two corn snakes in his back pockets on his return from a holiday in Thailand, was sentenced to three months in prison but got out this month after serving only six weeks.

If snakes were to become established in New Zealand, they could wipe out many of our native frogs, birds and reptiles. According to Mandy Tocher, a Department of Conservation herpetologist (snake expert) based in Dunedin, New Zealand's native animals could be vulnerable because they have not evolved to deal with such predators. And the snakes could also transmit parasites and disease to native reptiles.

"And they bite," she says. "And it costs money to have anti-venoms ready to go and the experts trained to deal with snake bites."

Kevin Hackwell, from Forest and Bird, agrees. "New Zealand's fauna has evolved over millions of years in the absence of mammals and snakes," he says. "They are not adapted to avoiding predation by these animals and are therefore particularly susceptible to their introduction."

But why not in put them in zoos where at least our Kiwi kids could get a chance to see the real slithery slimy thing? "In case they escape," says Tocher. "The risk is too high."

The parents of little Shaiunna Hare didn't hear a thing. The snake moved silently through the house while they were sleeping.

When they rose in the morning and checked the 2-year-old's cot, she was not breathing. A 2.6m-long albino Burmese python lay wrapped around her body.

The southern stretches of the United States are home to dozens of native species of snakes. Many, like the corn snake, are harmless. Some, like the venomous rattlers and water moccasins, are more dangerous. Love them or loathe them, they all belong and have their place in that ecosystem.

The Burmese python does not - it hails from Southeast Asia. So how did a python come to be in Shaiunna's Florida bedroom last year?

The python, along with a boa constrictor named Dixie, was a family pet.

That same week, thousands of miles away in Bristol, United Kingdom, a 4-year-old tabby cat was killed by a Burmese python as it wandered outside to a neighbouring backyard.

"We don't know whether Wilbur stumbled across the snake and it was an opportunistic kill or if the snake was actively hunting him," says owner Martin Wadey on his website.

"But either way, we heard the python's strike from the terrified scream that came from Wilbur and the subsequent blood-chilling cries as he fought for his life."

It was over in less than a minute. Wilbur was consumed whole. His killer, a 4m-long 80kg snake named Squash, had been left outside unattended in an unsecured property while his owner reportedly tended to his laundry.

In North America and the UK, where snake imports are not as restrictive as in New Zealand, having an exotic python means little more than a trip to the local pet shop or a search online. Increasingly, citizens of affluent nations with a little spare change in their pockets are looking for pets a little more exciting than poodles - and they are turning to snakes.

Hollywood A-lister Angelina Jolie embraced a boa constrictor on German TV. And pythons feature in Las Vegas stage shows.

But the tales of Burmese pythons show why snakes are best left elsewhere.

The first Burmese python was discovered 30 years ago in the subtropical swampland known as the Florida Everglades.

Since then, they have killed 12 people in the US - including five children - and injured many more.

Tests on captured snakes reveal genetic similarities and suggest a common ancestor. There is debate about actual numbers. Some say there are no more than 1000; others put the figure as high as 150,000.

By all accounts, the snakes are doing well. These opportunistic feeders, which can grow to 5m over a lifespan of 20 years, are feasting on endangered wildlife. At stake is a fragile ecosystem. So how did they get to the swampland?

Every year more than 200 million exotic animals - from kangaroo to kinkajou - are imported legally into the US. Many more enter through the international black market making Americans the biggest consumers of illegally traded animals in the world.

Mike Van Nostrand is the owner of Strictly Reptiles - the planet's largest reptile import-export company. He is also a convicted reptile smuggler.

He says Burmese pythons started arriving in the US in the 1970s. And after Vietnamese borders opened up in the 90s, "they poured in" - as many as 112,000, according to the US National Park Service.

Now most snakes are home-grown, produced by registered breeders. And in the Everglades, they reproduce on their own.

Despite their bad press and fear factor, Burmese pythons are a favourite among snake lovers. If not exactly affectionate, they are docile in nature.

But they can grow to a substantial length, weight and strength in a relatively short period of time. Because of this, many are abandoned in the wild.

Even island states are at risk. Guam, like New Zealand, had no snakes in the early 20th century. Now it has more than 20 snakes on every 2ha - one of the highest serpent densities recorded anywhere in the world.

After being subjected to devastating bombing during World War II, Guam began importing timber from New Guinea to help rebuild. One too many brown tree snakes went along for the ride. As the snakes made themselves at home, a disaster began unfolding. Having evolved in isolation from mammal and reptile predation, Guam's wildlife was ill-prepared to handle the new intruders.

Sixty years later, most of the birds are gone. So are two of its three native mammal species and half its lizards. And because those birds, mammals and lizards helped pollinate the trees and flowers, those are suffering too.The snakes have wreaked havoc on the electrical grid, causing frequent power outages and costing millions every year. And the mildly venomous creature is a threat to locals' quality of life.

For Guam, like Florida, dangerous snakes are now a fact of life. So if New Zealand quarantine inspectors seem cautious, perhaps it is with good reason.

Border Patrol:

At least 400 pests including insects, snakes, frogs and spiders are known to make it through border checks each year.

Possum: Estimated population of 50 million after first being brought from Australia in 1837 to establish a fur industry.

Rats/mice: We had no native species. Polynesians introduced the kiore rat about 1250AD. Norway rats arrived with European ships in the late 18th century, and ship rats in the late 19th century.

Rabbits: Brought to New Zealand for sport and food in the 19th century, they had bred out of control by the 1870s.

Stoats: Imported from UK to control rabbit population but by 1910 they had helped wipe out enormous numbers of native birds.

Cats: Introduced by Captain James Cook, the explorer, and also released into the wild in the 1870s to help control the rabbit population.

Deer: Introduced between 1851 and 1923 to provide game for sport, they prevent the regeneration of forests.

Goats: Gifted to Maori by James Cook, they were later used to control blackberry, gorse and briar. Grazing of forest thins undergrowth.

Pigs: Introduced by early explorers. Destroy forests.

Wasps: German wasps arrived in 1945. In beech forests, they take up to 90 per cent of the honeydew, depriving native birds, bats, lizards and insects of this vital winter food.