They say that what doesn't kill you makes you stronger - and that's certainly the case for "super rats".
These giant rats have become immune to normal poison bait, to the point where they feed off the toxic pellets to grow larger. Many are now as large as cats, and breed like rabbits.
Fortunately, a New Zealand-UK joint venture has spent more than 10 years developing a solution - spraying rats with a vitamin D formulation. The rats die of a heart attack within 48 hours.
The PiedPiper (Supplied)
Peter Signal, a director of New Zealand company Advanced Animal Technologies (AAT), says it's the combination of the chemical formula with a specially designed delivery system, called PiedPiper, that does the trick.
"We haven't run trials in New Zealand, but are moving to register it here and in Australia so it can be deployed," Mr Signal says.
"There are significant advantages over multi-feed bait or snap trap systems as PiedPiper delivers an exact lethal dose in a single application."
Rats are attracted into the shell by pheromones. When the rat trips the movement sensors, the processor activates the aerosol spray. A lethal dose of the chemical sprayed onto the rat's back is absorbed through its skin in 15 to 20 minutes. One can eradicates up to 250 rats before replacement is needed.
The inside of the PiedPiper (Supplied)
The formula includes cholecalciferol, better known as vitamin D3, and used as a health supplement in humans.
"'Super rats' are developing and becoming poison-tolerant due to the multi-feeding of toxins," says AAT owner Steve Goode.
"The alternative physical trap methods are generally considered too labour-intensive, needing servicing and rebaiting after each trigger event."
Mr Goode says the PiedPiper system leaves no environmental residues, unlike anticoagulant poisons, and has low toxicity to other species, solving the problem of secondary poisoning.
AAT hopes the system will help with the Government's plan to eradicate all pests threatening native birds and species by 2050.