Don’t have any monarch butterfly caterpillars on your swan plants? I haven’t for a while, which has given the plant a chance to recover, but neither have I seen wasps which predate on every stage of the butterfly’s life.

Mary Parkinson, who founded and runs the butterfly garden at Te Puna Quarry Park, tells me that wasps are probably the culprits though – they don’t change their diet until about the end of February.

Passion-vine hoppers (fluffy bums) will also eat the caterpillar and chrysalis and although they’re about in smaller numbers than last year, they’re still about.

Mary advises moving potted swan plant indoors or covering the plant (mosquito netting, fine-mesh shade cloth, old net curtain) as there are likely to be eggs on it. “The trick is to protect caterpillars as much as possible. I have even seen an ant carry off a tiny caterpillar.”

The fine seeds of a swan plant – if you snap off the pods before they open you won’t have plants coming up everywhere. Photo: Sandra Simpson

If you suspect you have too many eggs for your swan plant to support, wipe some off and cover the plant – it won’t stop more eggs being laid but it will reduce the number able to be laid.

Pumpkin shouldn’t be used for supplementary feeding until the caterpillars are in the end part of that stage of their life (2cm long or more). Younger caterpillars fed pumpkin will emerge from the chrysalis with deformed wings.

“It’s easy to underestimate how much a caterpillar will eat,” says Mary, a member of the Monarch Butterfly NZ Trust. “But the faster they eat, the faster they’ll go into the chrysalis stage.”

A monarch feeds on cherianthus (wallflowers). Photo: Sandra Simpson

Any garden that wants to support a butterfly population must be spray free and must provide nectar all year round – old-fashioned flowers in strong colours is the general rule of thumb.

The butterfly garden at the Quarry has a new butterfly house – much roomier. Mary moves her caterpillars indoors so they build their chrysalis and emerge inside before being released into the garden.