A teenager has been sent to prison for three months after smuggling two small snakes into the country in his pants.

Michael Luke Mullany, 19, is inside Auckland's Mt Eden Prison after a judge told him "anybody who brings snakes into this country can expect to go to jail".

The sentence at Auckland's North Shore District Court this month has been greeted as a hard example for anyone trying to beat the nation's border security. But the teen's family told the Herald on Sunday they were devastated he had been put in prison.

Mullany's dad, Jim, said: "I don't understand it. We're pretty disappointed about it."

Mullany was only 18 when he went on a holiday with his mother to Bangkok, where he bought the brown and cream mottled corn snakes at the Chatuchak Market. The snakes are not poisonous.

Court papers show that Mullany kept the snakes in a box in the hotel he and his mother were staying at - and he told her he had returned them before the trip home.

Instead, Mullany boarded the return flight to New Zealand with the snakes tucked into his rear trouser pockets. "During the flight he sat on the snakes, careful not to squash them but to keep them warm," said the prosecution case.

He later told investigators he "just slouched on the seat". Mullany said he knew they ate mice, weren't dangerous and intended to do more research when he got home.

At the airport, Mullany filled out forms saying he was bringing nothing in that was banned, despite walking past a slew of signs and warnings.

Once back in the country, Mullany tried to set the snakes up at home in an aquarium, travelled with them to Tolaga Bay to visit his father and then decided he would sell the snakes on the internet. That proved his undoing.

He told investigators he "couldn't bring himself to kill them and didn't want to set them free because that would be stupid", court papers said.

His offer on a website for tropical fish enthusiasts alerted Ministry of Agriculture and Forestry staff who arranged a sting.

Mullany was promised $2200 for the snakes. Minutes after meeting the buyer and doing a deal, officials arrested him.

MAF enforcement director Jockey Jensen said the prison sentence was a warning to anyone bringing snakes in.

He said snakes posed a potential threat to the nation's environment. It was impossible to predict the eventual impact of any alien species introduced.

* 2 Baby Corn snakes smuggled in teenagers trousers
* 3 Number of months he was sentenced to
* 5 Number of years he could have faced in jail.