It's a new phenomenon which has monarch butterfly experts concerned.
Jacqui Knight, of The Moths and Butterflies of NZ Trust, says they are seeing fewer, if any, monarch butterflies at the moment and some of those they are seeing are not laying any eggs.
But what it means for the eco-system is unknown, lepidopterist Brian Patrick says.
Knight and Patrick, who is also the trust's consultant scientist, are asking New Zealanders to help them work out why the butterflies are so scarce; whether it's something to do with their habitat, a wetter than normal winter or something else completely.
Knight said she first started noticing fewer monarchs in February last year.
However, the scarcity of them in December was alarming.
"I did contact weather forecasters last year and we couldn't correlate the data with any weather patterns.
"I've got to do a lot more homework before I can say what it could be.
"In 50 years of studying monarchs I have never witnessed this before."
On Tuesday, Knight noticed one monarch fly into the backyard of her Auckland home and onto her swan plant, only for it to circle and take off again.
"They've all been raised organically unless there was spray drift from say, council spraying in the street, but I've got no idea at this point in time as to what it could be."
When the monarchs came back in the spring she had one good round of them laying eggs then they all died.
"That can happen because the first monarchs who come back to your garden they lay eggs and then they die so you've got at least 28 days before you've got more adults to lay eggs. But when I did have those adults that's when they weren't laying eggs.
"So I've just got to figure out why."
The butterflies assess the quality of the plant when they land, by sticking their two front legs into the leaf. If they aren't happy, they fly to the next one.
"I put everything in to make [swan plants] perfect and it's just not happening."
She's called for feedback on the trust's Facebook page, the majority of responders also say they haven't seen as many monarchs this season.
However, she also wants to hear from people who have been seeing the butterflies.
Patrick, of Christchurch, said it was hard to know whether the drop in numbers was because of predators - the German and common wasp - or the wet winter.
"There's something odd going on this year. When I was in the Christchurch botanic gardens the other day I saw a rare sight for this season, I saw four monarch butterflies in one spot.
"That's a lot for this year. It's normal for other years, but we're just not seeing them.
He said the fact there weren't as many around and the fact they were not laying eggs "could be related".
"Not too many of them could mean females are finding it hard to find a male to mate with. But honestly, we don't know what the answer is.
"It has been a very odd weather season, it's a very wet season, up and down the country."
They did know that the "over wintering" - a form of hibernation - spots had been inundated with wasps and rats.
Come spring the butterflies move around, mate and the females lay eggs. But the process was for some reason being stymied.
Patrick said they had no idea of the implications of what was occurring as it had not happened since the insects first landed in New Zealand in the mid 1800s.
He was not aware of it happening anywhere else in the world.
* People are urged to report sightings or fewer than usual sightings at www.mb.org.nz