Pumpkins will save the monarch butterfly

People rearing monarch butterflies can try food sources other than the ever-diminishing supply of swan plant leaves.

The plants, particularly smaller ones, frequently have their leaves stripped from them by ravenous caterpillars before they develop into their chrysalis stage.

With more and more butterflies appearing as summer draws to an end, Landcare Research has advice for people seeking other food sources.

Landcare entomologist Leonie Clunie said that although swan plants were still the ideal source, one option was to place large fat caterpillars that had eaten themselves out of swan plant leaves on a slice of pumpkin.

But pumpkin was no good for younger caterpillars.

"This is not the best food for them ... It may tide the bigger ones over but the younger ones won't survive."

Mrs Clunie said the pumpkin was probably a source of moisture for the bigger caterpillars rather than a source of nutrients.

People could also transfer large caterpillars to tweedie, a common garden plant with a small blue flower. The weed moth plant was also a nutrient source for small and large caterpillars although adult monarch butterflies will not lay eggs on it.

Moth plants can mean life - and death - for monarchs. The flowers can trap the mouthparts of feeding butterflies, which then die slowly from exhaustion and dehydration.

Monarch butterflies are native to Californian coastal regions and are thought to have arrived in New Zealand naturally.

The earliest European record of the butterfly in New Zealand dates from the 1880s.

Because monarch butterflies eat only introduced plants, they have no known harmful effects on New Zealand ecosystems.

Landcare Research