MBNZT chair Rebecca Bibby said the trust had fielded reports of "too many caterpillars" in places like Hamilton, not usually known for its tropical weather, and another report of an early monarch in Southland. But in Northland, Auckland and the Bay of Plenty there were few butterflies about.
The MBNZT is urging everyone to look out for social wasps in gardens and to ensure nests are found and removed before wasp numbers build up. These wasps are a problem for humans, livelihoods and native flora and fauna.
"If wasps are affecting our monarchs, then our native butterfly population and other invertebrates will be affected," Ms Bibby said.
New Zealand's Lepidoptera displays the world's highest rate of endemism with the majority of species, 92 per cent, found nowhere else.
"There are many organisations working to protect kiwi, kokako and even giant snails, but New Zealand has very few species of Lepidoptera and they are becoming less known each year."
Lepidopterist Brian Patrick gives an example of a tiny purple copper butterfly which exists only in one coastal car-park in the South Island.
"It's teetering on the edge of survival," he said.
"The plight of our butterfly fauna is heavily dependent on human action if they are to survive and thrive. There are many moths and butterflies that are threatened with extinction even before they are described."
The MBNZT also urges people to grow swan plants now so that when the monarchs do visit gardens, there are plenty of host plants on which to lay eggs.