It was good news - but it could also be bad news.

One of the largest of the rat species, Rattus Norvegicus - the Norway or brown rat – has been killed in a trap on Mauao, lured there by an offering of peanut butter.

'I am always stoked to see one of those in the trap, it's always a bonus,” says Julia Graham of the Western Bay Wildlife Trust. 'Because they can be notoriously trap shy.”

The rat was as long as her forearm and weighing probably half a kilogram. They can grow to a kilogram, as big as the Blue Penguins they attack.

Does one rat in a trap mean there are probably more?

'Definitely. If there are no rats in the other traps we would like to think that's because there are no more out there. Or does it simply mean we haven't caught them. It's a catch 22 situation.”

The Norway rat is a deadly menace, a threat to everything says Julia.

'They eat the eggs of the Little Blues, they eat the babies and they will attack the adults.” They are also a threat to lizards, skinks and geckos and wetas. 'They are big rats and they eat a lot of food.”

'We still have to check the other bait lines. We would expect there to be more rats. After all spring has sprung.”

And Julia wants to remind us that we can help. 'Be smart,” she says. 'Anytime a rat gets food off a human you are just assisting it to get bigger and stronger, to have more babies and become a bigger menace.”

So do not leave picnic litter on or around Mauao. Even an apple core is enough to encourage a rat. 'They love any sort of food,” warns Julia.

If you live in Mount Maunganui ensure your compost is sealed against rats, ensure grains and chicken food are kept in sealed container and don't throw out bread for the birds because it could become food for the rats. And keep rubbish bins covered, inaccessible and empty.

Tauranga City Council parks ranger David Grimmer with the dead intruder. Supplied Photo.