A Frenchman who told airport border staff that his gumboots had been bleached clean, has been fined $400 after they were found to contain a stowaway snail and were covered in goat poo.
The passenger arrived at Auckland airport on a flight from Papua New Guinea earlier this month.
He initially said he had scrubbed the boots with bleach.
But on inspection, they were found to be contaminated with manure from a goat farm.
And a Ministry for Primary Industries (MPI) quarantine inspector was stunned to find a snail inside the boots when cleaning them.
"The boots posed high biosecurity risk to New Zealand,'' said ministry team manager Paul Ruttley.
"If they had only been used on the street in the city, it would have been okay.
"But, as they came from a farm, they could have been carrying diseases with potential to have a devastating impact on our farming industries.''
The man was fined $400 for failing to declare biosecurity risk goods and the snail was "euthanised'', the ministry said.
Mr Ruttley says it is fairly common for MPI quarantine inspectors to intercept dirty boots, but very unusual to discover a hitch-hiking snail.
Cane toads from Australia have been found inside boots in the past, he said.