In NZ the natural food species of the Monarch (Danaus plexippus) larvae is the Asclepiadiae family – milkweed which includes swan plant (Gomphocarpus fruticosus) and giant swan plant (G. physocarpus) as well as Asclepias species such as tropical milkweed/bloodflower (A. curassavica). The tropical milkweed comes in two colours -scarlet (which has a gold centre) and gold (all yellow).
The term ‘milkweed’ can be confusing – but a Fact Sheet on this is available. The Monarch Butterfly NZ Trust will be able to help you with seed of the giant swan plant and tropical milkweed, each packet is $5.
Larvae in their latter stages can sometimes be fed on a noxious weed called moth vine, cruel vine or kapok plant (Araujia sericifera) and some people have had success with cucumber, pumpkin and courgette – but only when they are in their last instar, i.e. ten days old or more than 2cm in length. Any earlier than this and the larvae will not get enough cardenolides (chemicals called cardiac glycosides) and will not be able to make a successful transition to an adult.
Moth vine is on the banned list in some regions – check with your regional council.
When caterpillars have eaten all the leaves they will then eat the stems and fruit (seed pods). You can crush the ends of the stems while you sort out a long-term solution. Don’t let them wander away!
*** If you have “run out of food” place a notice in the forum but make sure to say where you live. Someone in your neighbourhood may be able to help!***
Adult butterflies need plants giving nectar. They usually choose flowers with bright colours, purples, pinks and blues in mass plantings. Buddleias and Hebes are very popular. There are more listed in our forum – click on the link on the homepage to go there. There is a poster showing many nectar plants available from the MBNZT. See it here.