Monarch butterfly lovers up and down the country are worried. Each year there appear to be less monarch butterflies gathering at recognised overwintering sites – but it is very difficult to quantify the actual numbers.

In North America, the monarch is known for its amazing annual migration. East of the Rocky Mountains, the butterflies can fly more than 4,500 km in search of their overwintering haven high in the Mexican mountains. They wait there in huge numbers until the spring and then begin flying north as the weather warms up, the numbers multiplying as they go.

Monarchs also overwinter in various locations in NZ, no doubt since they first arrived here in the 1800’s.

“Most butterflies spend winter as larvae or pupae, waiting to emerge as a butterfly in summer,” said Professor Myron Zalucki from The University of Queensland. “Monarch butterflies, however, spend winter as adults, which gives them a head start for the mating season in spring.”

“New Zealanders have had a love affair with the monarch butterfly ever since I can remember,” said Jacqui Knight, Founding Trustee of the Moths and Butterflies of NZ Trust. “Way back in 1986 I was trying to find out where monarchs overwintered in NZ. People all over NZ sent hundreds of letters, even including maps, but all that correspondence was lost.”

In 2005 the Christchurch City Council published a map of known overwintering sites in Christchurch. Five years later, after the earthquake, some of those sites were no longer in use.

“When the MBNZT was established almost twenty years ago it was to protect a recognised overwintering site, but we found that the monarchs no longer went there in large numbers. And today we are seeing much smaller numbers in other overwintering sites.”

She mentioned two that she visits each year: Jellicoe Park in Onehunga and the Blockhouse Bay Recreational Reserve, where this year numbers are very few. And it’s the same in other parts of the country.

“The monarch is so well known in NZ,” said Maurice Mehlhopt, MBNZT Chairman. “It’s large, beautiful and mysterious and easy to enjoy in the garden. Most NZ children have learned about the monarch life cycle at some stage in their lives.”

Dr David James from Washington State University, who began his career in Australia, is interested in what is happening in NZ as well.

“The population in South Australia appears to be more robust than other parts of Australia,” he said. “The milkweed they use, Gomphocarpus cancellatus (wild cotton), used to be rare but now it’s common and widely distributed.”

Monarch-lovers are encouraged to monitor known sites and send information to trust@nzbutterflies.org.nz. Ways to help the monarch butterfly population is on their website. Information can be sent to trust@nzbutterflies.org.nz.

“We are asking for people all over NZ to send in information about known overwintering sites so we can add this information to our website,  www.nzbutterflies.org.nz.”

In 2025 the MBNZT will be asking citizen scientists to tag monarch butterflies so that more can be learned about their overwintering behaviour.

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