Monarch butterflies do not seem to be about in their usual numbers this year. Researchers are to meet in Auckland in March to figure out what has happened to them.
The monarch butterfly is synonymous with New Zealand summers.
"We've heard from many monarch lovers in Canterbury and Otago that the monarchs haven't returned this summer - and it's something that's got us baffled," said Monarch Butterfly NZ Trust secretary Jacqui Knight.
It is thought that a tough cold winter across the South Island dampened breeding numbers, AAP reports.
"Just what that is, though, we need to figure out," Ms Knight said. "We love the monarch ... It's a wonderful, beautiful insect and one we really need to look after."
She believes pesticide spraying is also a problem.
Experts say the anecdotal decline could be an indicator that times are tough for other insects.
"Monarchs are an indicator species, telling us a lot about how other insects are going, and this is something to watch closely as we need our insects," Ms Knight said.
The conference at Unitech on 16 and 17 March will also discuss some of New Zealand's less visible species.