BOUNTY HUNTERS: Enner Glynn School pupils Toby Walker, front, Alice Dowse and Alex Wilson, with Nelson MP Nick Smith, promote the $10 bounty on great white butterflies.

Wanted: Dead, not alive. A bounty has been placed on Nelson's brassica-eating, eco-crime committing great white butterfly.

The Department of Conservation has offered a $10 reward for every dead adult great white butterfly brought to the Nelson DOC office during the two-weeks school holiday, starting on Monday.

"We want great white butterflies dead not alive," Conservation Minister Nick Smith said, announcing the new initiative at Enner Glynn School this morning.

"They are an unwelcome pest and pose a major threat to endangered native cresses and garden and commercial plants like cabbage and broccoli."

Nelsonians are encouraged to grab a butterfly net and head outdoors in pursuit of the now potentially lucrative pest.

Dr Smith said it was sensible for children to be on the front line in the fight against the great white, as catching bugs and butterflies had long been a youngsters' speciality.

"I remember being a 7-year-old and getting a butterfly net for my birthday," he said.

Although he recalls trying, and failing, to capture a majestic monarch, Dr Smith said he caught plenty of moths in his limited time as a butterfly hunter.

He hopes the $10 incentive will inspire the next generation of bug-catchers and help to eradicate the great white blight from the Nelson area.

"To date they have only been found in Nelson Tasman but we must do everything we can to ensure they don't become a permanent widespread pest," Dr Smith said.

"Female great white butterflies can lay as many as 750 eggs, so every butterfly killed potentially stops up to another 750 butterflies emerging.

"The peak period for the butterflies emerging from pupae this spring coincides with the school holidays. It's a great opportunity to involve school children in conservation, as well as earning some extra pocket money."

Eradication project manager Bruce Vander Lee said DOC staff could not be everywhere at once, searching the region's 20,000 properties that were likely habitats for the butterfly.

He said having the public join the hunt would improve the eradication campaign's likelihood of success.

The project's two-year budget of $2.6 million provided enough capital to reimburse even the best and most successful butterfly hunters, Mr Vander Lee said. He was confident that the bounty offer would help DOC destroy the environmental and economic threat posed by the great white.

"If you look at the risks if we don't beat this thing, it's certainly worth a go," he said.

Dr Smith told pupils at Enner Glynn that great whites were mostly found in the Port Hills area of Nelson, and had also been seen as far out as Stoke and the Glen.

He encouraged the children to visit Nelson's parks and reserves, but said they must ask permission before going next-door into their neighbours' vege gardens.

"It can be difficult to tell great white butterflies and small white butterflies apart but it doesn't matter if small whites are killed as they are also a garden pest," Dr Smith said. "DOC is still asking people to bring in small white butterflies to double check they are not great whites. Although the $10 reward won't be available, those who drop them in will go in a draw to win spot prizes."

THE BOUNTY

While children are encouraged to start hunting during the school holidays, the $10 per butterfly bounty is offered to adults, too.

Butterflies should be sealed in a jar or plastic bag and stored in the freezer, so they don't go mouldy, until they can be dropped off at DOC's Nelson office on weekdays between Monday, September 30, and Friday, October 11.

The bounty will not be available at other times and is only for adult butterflies