It is perhaps New Zealand’s most identifiable butterfly, but the monarch is in decline and the cause could be the swan plants people buy to attract them.
The global population of monarchs has declined by 80% and experts fear the figures could be similar across Aotearoa.
Many people buy swan plants – which are a type of milkweed – to encourage monarch butterflies as they like to lay their eggs on the plants.
However, instead of helping the flying insects, the plants could be contributing to their fall in numbers, as some have toxic pesticide on them which are harmful to the caterpillars.
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“Last summer, several people who bought swan plants in Wellington to feed caterpillars had all their caterpillars die,” said Jacqui Knight, founder of the Moths and Butterflies of New Zealand Trust.
“A plant was forensically tested and found to have two insecticides and one fungicide on it.
“The store had assured the customer that the plant was pesticide-free. It clearly wasn’t.”
Commercial growers use pesticides when producing swan plants in large quantities, to protect them from pests.
People who want to attract monarchs are encouraged to grow swan plants earlier in the season and let them get to full size in their garden.
Alternatively, people should keep the plants protected from the monarch butterflies until they are free of pesticide.
In 2018, swan plants were so in demand there was a national shortage, with one store selling out as quickly as they could get the plants in.
The monarch is originally from North America but was first recorded in New Zealand in the mid-1800s. It is considered a native because it flew or was blown here.
New Zealand is home to 26 types of butterfly. Others include southern blue, Harris’s tussock and black mountain ringlet.
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