Moss balls "have the potential to ruin the lakes and rivers of New Zealand", but are readily available on AliExpress.

Buying a prohibited plant or animal from overseas has never been easier.

Whether it makes it into the country is another matter, but the cornucopia of online retailers means unwitting consumers are never more than a click away from causing the next biosecurity threat.

Internet shopping is a relatively new front in the war to keep New Zealand free of unwanted species, but the risk it poses continues to grow as more people head online.

123RF.COM Marimo moss balls are algae with a velvety appearance that are found mostly in lakes in the northern hemisphere. They are protected in Japan.

NZ Post figures show the volume of international parcels - both inbound and outbound - increased by 17.8 per cent from 2016 to 2017 to more than 23 million parcels.

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With limited information on what species can and cannot be brought across the border, consumers ignorant of the threat posed by their purchases are falling afoul of the law.

IAIN MCGREGOR/STUFF Raquel Miranda told the Christchurch District Court she was unaware the moss balls were illegal to bring in, while her defence maintained even if she had checked the MPI website she would be none the wiser.

The Ministry for Primary Industries (MPI) recently prosecuted Christchurch botanic artist Raquel Miranda for illegally importing marimo moss balls through online Chinese store AliExpress.

Miranda told the court she was unaware the moss balls were illegal to bring in, while her defence maintained even if she had checked the MPI website she would be none the wiser.

"It may be that as a result of this case and the deficiencies you have pointed out, they may change their website," Judge Jane Farish said.

"Marimo moss balls have the potential to ruin the lakes and rivers of New Zealand if they were allowed to be introduced."

Another Christchurch woman, Melanie Stevenson, who also unwittingly imported moss balls through AliExpress, saw coverage of the case and freaked out.

"Honest to God, I thought 's..., am I going to go to jail as well?'"

"I just read that it was illegal and that they've been imported to the country, but I couldn't work out how that could happen considering they went through Customs."

MPI compliance manager Garry Orr said while MPI staff did their "level best", it would be "naive to think we stop everything coming across the border".

There have been calls for clearer information or education campaigns to help the public know what can be imported, but Orr said publishing a list of all allowed or unwanted species was too difficult.

"Covering every plant species and animal species around the world would be nigh on impossible to maintain and keep updating," he said, comparing the scale of the project to the Encyclopaedia Britannica.

MPI does publish the Plant Biosecurity Index, a register of close to 30,000 approved species and requirements for importing them, but Orr said people should not rely on what was online and instead call the ministry if they had any doubt.

"We do say to people biosecurity is not just the responsibility of MPI as the regulator, it's the responsibility of every New Zealander - if we want to protect the environment we all have a role to play."

Given the damage non-native species have caused in New Zealand, invasion biologist Dr Ian Duggan said he was always surprised people did not think twice before buying them in from overseas.

The University of Waikato academic said, while some people deliberately flouted the laws, many people would be ignorant of what they could buy online, and more information would be helpful.

"If we are now in a world of online shopping, why should the information regarding what can be brought into the country not also be clear and online?"

He advised people that if they could not find information that an import was allowable, they should assume it wasn't.