Wasps a Royal Pain

Wasps a Royal Pain

The Moths and Butterflies of NZ Trust is concerned at the apparent scarcity of Monarch butterflies overwintering this year.

“While Monarch butterflies are not indigenous to NZ,” said Ms Rebecca Bibby, Chair of the Butterflies Trust, “if Monarchs are suffering from environmental effects then you can be sure our other invertebrates are also being affected.”

The last Monarchs of each season, in the autumn, will overwinter in trees such as in parks and on golf courses, and then at the end of the winter they return to gardens to reproduce, starting the next generation.

Each year in March and April citizen scientists throughout New Zealand tag and release Monarch butterflies. Each butterfly is given a unique number and people finding tagged Monarchs can log the sighting on the Trust’s website. The data gives an indication of the age of the butterfly, how far it has travelled and how long the journey took. The team of citizen scientists or taggers have reported that there are less Monarchs around to tag, so consequently there are less Monarchs overwintering.

According to an overseas study invertebrate numbers worldwide have decreased by 45% on average over a 35 year period. Such a decline is of concern because of the enormous benefits butterflies and other ‘small creatures’ bring to our day-to-day lives, including pollination and pest control for crops, decomposition for nutrient cycling, water filtration and human health.

“People are noticing the absence,” said Ms Jacqui Knight, secretary of the Trust. “I have been to several of the usual overwintering sites around the country and have found very low numbers of Monarchs.”

She says that part of the problem is the enormous build-up of social wasps over the past two warmer winters.

“When wasps are looking for protein to feed their young they take Monarch caterpillars. This has badly affected Monarch numbers.”

But she added that what is happening to Monarchs will be affecting other invertebrates too. “Many of our members raise Monarchs under cover now to keep them safe from wasps,” she said. “But our other invertebrates, many of them unique to NZ, are also at risk – and we can’t protect them all.”

The Trust is working on initiatives to reduce social wasp numbers and hopes that people will also reconsider before cutting down mature trees. As well, they urge members of the public to report sightings of Monarchs, especially overwintering clusters, on their website www.mb.org.nz.

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