A venomous snake, spiders and a pair of scorpions are just some of the serious biosecurity hazards to have breached New Zealand's borders in the past four years.
But of the 546 incursions recorded, only 176 have prompted officials to move to eradicate the pests, figures released by the Ministry of Primary Industries (MPI) under the Official Information Act show.
A large species of diamond python discovered in Auckland is one off 54 incursions recorded so far this year. It is unclear where the python came from, but the snake was destroyed.
A common brown snake, considered to be the second most venomous land snake in the world and native to Australia, Papua New Guinea and Indonesia, was dealt with after being found in Mid-Canterbury this year.
Biosecurity officials' attention had been called to Mid-Canterbury four years earlier when a marbled scorpion, native to Australia, was found there. A second marbled scorpion was also found in the Otago Lakes District that year.
Biosecurity officials did not move to eradicate the scorpions but the MPI said in cases where pests weren't part of a breeding colony or posed no risk to New Zealand's ecosystem, no action was taken.
Veronica Herrera, the ministry's response and investigation and diagnostic centre director, said it received a "steady flow" of information on potential biosecurity threats.
"It investigates these and determines if there is, in fact, likely to be a breeding population present and if the situation warrants a full response to attempt to eradicate or control the organism.
She said only a small percentage of the organisms found were part of a breeding population.
"And of those, not all present a significant economic or environmental impact as to require action by the ministry."
In 2010 there were 16 lizards that biosecurity teams had to deal with, as well as four foreign frogs, which managed to get inside New Zealand.
Ants, mites and types of fungus were also common invaders.
While some of these entered the country unintentionally, the MPI had successfully prosecuted a number of people over the past four years for deliberately trying to import foreign animals and plants.
In February this year, two people were prosecuted for packets of seeds and plant cuttings which did not belong in New Zealand. In 2010, Van Minh Ho was convicted for importing four Vietnamese Fighting Fish.
Auckland University conservation and ecology professor Mick Clout said New Zealand had a "world-leading" biosecurity system.
"We understand the importance of it, and we tend to take it far more seriously than many countries."
Clout, who also chairs the Biosecurity Ministerial Advisory Committee, said it was important for two reasons.
"First our economy relies so heavily on primary industries and secondly, we are relatively pest free which has allowed some very unique wildlife to thrive."
Among the destructive organisms and diseases which have made it into the country and successfully spread are the varroa mite, which is an external parasite of honey bees, and the PSA virus which attacks kiwifruit plants.
The painted apple moth and southern salt marsh mosquito were established in New Zealand, but costly spraying exercises had eradicated both species.
A single male Queensland fruit fly was discovered in Auckland earlier this year, but the ministry found no evidence of any more.
About $1.5 million was spent making sure the fly was the only one, with Horticulture NZ saying the damage to New Zealand's $4 billion horticulture industry could have been far greater had the fly successfully spread.
Horticulture NZ has been openly critical of biosecurity systems in New Zealand, because not every person flying into the country has their luggage x-rayed.
Despite this, MPI figures show over the 2010-11 financial year, five million passengers flew into New Zealand. At risk goods, which could potentially bring biosecurity hazards into the country, were seized off 112,329 of those passengers.
Across a 24-hour period at Auckland Airport, biosecurity teams seized 100kg of fresh fruit, 700kg of meat and 100kg of seeds.
Herrera said from time-to-time unwanted organisms did slip through the net, but thousands of pests and viruses were kept out of New Zealand.
"No biosecurity system can stop everything and this is why we have a multi-layered biosecurity that starts off-shore, provides strong border protection on-shore, and then provides and effective surveillance, pest management and eradication capability inside New Zealand to deal with those things that do get through.