More than ever before monarchs need our help. In North America deforestation, pesticide use, GM crops and climate change are affecting numbers. The destruction of the native oyamel forest in Mexico for avocado farming is affecting the overwintering sites.
And monarch populations are struggling here in NZ too: they are ravaged by social wasps, their major predator. But there are other considerations as well.
Here are some "Dos and Don'ts" on how you can help the monarch population in NZ.
- DO buy twice as many swan plants, and protect some for the monarchs of the future.
- DO make sure you have some nectar plants growing - for the monarchs and our other pollinators as well.
- DON'T plant new swan plants in the summer heat. Wait until the caterpillars have eaten the leaves, prune the dead stems, and THEN plant the the plant. (The plants will be stressed enough being eaten without having to cope with being transplanted.) Plant what’s left when the leaves have been eaten… but wait until it’s cooler (evenings) and keep it well-watered.
- DON'T handle caterpillars. You may have sunscreen or cosmetics on your hands, for example. Observe the life cycle but minimise handling. Monarchs have been undergoing metamorphosis for millions of years without the help of humans.
- DO let caterpillars move themselves to the new plant, if you "buy more food". Put the new plant next to the old one, or cut the stems with caterpillars on and lay the stems at the base of the new plant. New plant(s) may not immediately appeal to your caterpillars and it could be that the toxicity is at a different level to that in the plant it was eating. Water the new plant well to rehydrate it.
- DO grow your own plants from seed – that way you will know for sure whether the leaves are safe for caterpillars. Buy seed anywhere you see Yates products. Yates gives the MBNZT a donation for each packet sold. Plant seed now for later.
- DO grow plants on from previous years so that they are in their second season and over 1 metre tall. If they are fertilised, watered and mulched, the growth in the spring and summer will almost keep up with the caterpillars.
- DON'T remove seedlings that pop up in the wrong place. They can be left until you need food. Cut the stem close to the roots and split the cut stem before putting it in a container of water. Stand the container next to the plant.
- DON'T EVER feed them alternative foods such as pumpkin, cucumber or other members of the cucurbit family. Monarch caterpillars are meant to eat milkweed (e.g. swan plant) and many will not eclose into healthy butterflies when fed the wrong food. As well, there is a risk that we are doing long-term damage to their internal systems.
- DON'T move or disturb caterpillars when they are moulting. Caterpillars shed their skin (moult) five times. They may choose to leave the plant as they sense that is where predators and parasites will find them. When they are moulting they will spin silk around themselves and disturbing them may kill them.
- DON'T use pesticides. Fly sprays, plug-in insect controls and flea collars on pets can kill caterpillars. Sun-screen and cosmetics on hands can also affect them. New carpets and drapes can sometimes contain insect-proofing. Swan plants are NOT indoor plants. The humidity indoors could alter the toxicity level in the leaves and could poison your caterpillars.
- DO pinch out the growing tip when your plant is 15-20 cm, just above a node. The plant will now form two branches and bush out, creating twice as many leaves. A few weeks later pinch out the growing tip of the new branches. Also, a plant’s mission in life is to reproduce (set seed). Leaves feed caterpillars… flowers lead to seed. If you remove the flowers the plant continues to strive to fulfill its mission and as a result will feed more caterpillars.
- DO think about growing Asclepias incarnata or swamp milkweed if you are not "frost-free" (i.e. cooler area). The plant will grow from a rhizome in the second and ongoing years, and will sprout soon after the last frost. It is very quick-growing and is a very popular nectar source as well. Seeds are on our ‘Shop’ page.
- DO consider growing A. curassavica, the tropical milkweed, if you are in a warmer area. There are two varieties – one has scarlet/gold flowers and the other has yellow flowers. These add a bit of variety in your garden. Seeds are on our ‘Shop’ page.
- DO put a notice on our special Facebook Group: Monarch Matchmaker or in a network such as ‘Neighbourly’ if you have no caterpillars OR too many caterpillars, for others to help you out. You might even be able to help out a local garden centre that has too many caterpillars on its swan plants!
- DO remember that swan plants are poisonous so be careful when handling them. Monarchs store toxic steroids (known as cardenolides) from the swan plant and use them as a defence against some predators.
PESTICIDE USE
Commercial growers raise thousands of swan plants (a species of milkweed) and plants need to be in the best of condition when they are sold. Garden centres cannot sell plants covered with aphids, or bereft of leaves, so some growers use pesticides to protect their plants until they are sold.
Remember a female monarch can lay about 700 eggs (one was recorded as laying 1179). Caterpillars grow almost 3000 times in size over two weeks… so one day there are plenty of leaves and a day later the plant is just a stalk.
-
DO use garden centres that are confident their swan plants are pesticide-free, and that staff will be able to advise on nectar sources and host plants for other butterflies and moths.
Look out for the 'approved by butterflies' sign on their door or merchandising material.
Always ask at your garden centre 'is this plant safe for caterpillars?' If that person doesn’t know, ask them to find out. Garden centre staff should be aware of how safe the plants are.