Monarch butterflies disappearing from Nelson as paper wasps take hold
Two summers ago Nelson couple Chrissie Ward and Tony Staufer raised 460 monarch butterflies in their small Nile St courtyard garden and watched them flit away. Last summer 240. This summer so far, 17. They blame asian paper wasps and fear that the slaughter will get worse if people don't act.
Ward and Staufer are monarch butterfly enthusiasts and go to great lengths to provide the best conditions. They have dozens of the swan plants that the caterpillars feed on in various stages of growth and a high fence keeps out strong wind.
But now they have to do even more because if they don't deadly asian paper wasps will destroy the little creatures they so carefully nurture. The wasps will take the tiny eggs from the swan plants and also caterpillars at all stages of development, from when they are barely visible to when they are plump and ready to go into the chrysalis stage.
Ward, the Nelson spokesperson for the Moths and Butterflies of New Zealand Trust, said the same wasp invasion was wiping out monarchs across Nelson, most particularly in the Wood-Maitai area but in parts of the city too.
"They are very very bad - a plague," she said.
"Probably the warmer dryer weather suits the wasps and they're multiplying. Everybody's saying, 'My garden's full of beautiful swan plants, with nothing on them'."
She said monarch butterflies were special because they were unafraid of humans, and were an excellent way of teaching children about the metamorphosis from caterpillar to chrysalis to hatched butterfly. They were also good pollinators.
Staufer has become adept at catching the small wasps in a butterfly net, which helps. But the couple's main success now is through moving the eggs and caterpillars into a safe glass-topped enclosure with potted swan plants for them to feed on.
Ward said people could look around their gardens to find the small wasp nests.
"They are just decimating the monarch butterflies."
Staufer said in past years there would be six or seven monarchs fluttering around the garden at this time of year. Today they seldom see one arriving to lay eggs.
"Nowadays I pick up the smallest caterpillars before the wasps can get them."
However the caterpillars are prone to injury and should not be directly handled, instead moved on the foliage where they are discovered.
Asian paper wasps were first found in New Zealand in 1979. Longer and more slender than common wasps, they can be identified by the way their long legs trail behind them when they are in flight.
The trust says that the delicate little rounded nests, found hanging from eaves or trees and shrubs, can be sprayed with fly spray to kill the residents and later removed by cutting their attachment and dropping them into a bag. It warns, "Be careful as dying wasps may drop down and sting you."
Originating in North America, monarch butterflies found their own way to New Zealand and have become this country's most identifiable butterfly species.
Their survival depends on the availability of swan plants and other milkweed species for the caterpillars to feed on. As well as paper wasps, the caterpillars can also attacked by the praying mantis.
And if the Nelson population is in trouble, Ward and Staufer do have some good news. Golden Bay friends have told them that the wasps haven't made an impact there, and their swan plants are being munched by hordes of hungry caterpillars.
For more go to www.monarch.org.nz