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Despite their lofty status and poisonous bodies, there are some things that can cause problems to Monarch Butterflies and their larvae. But thankfully we can, with a bit of know how, make sure their needs are well served.
Monarch butterflies are fairly fascinating creatures whose larvae (caterpillars) are specialist herbivores of milkweed plants (such as swan plants). As soon as they've hatched, the caterpillars start to sequester the toxic cardenolides present in the plant, which works well as a defense mechanism as they quickly become poisonous and unpalatable to most predators.
However despite this, there are some pests that can cause problems to the caterpillars and the plants. But hopefully some of these handy tips will help.
The larvae go through 5 major stages (or instar) before they pupate fully and become butterflies. After each stage they moult, become bigger and the pattern on their bodies become increasingly complex.
While it's easy to help Monarch Butterflies flourish by growing swan plants a few things can go wrong. So here are a few tips to make sure that their reign is long and fruitful.
There are several wasps that will attack and kill the caterpillars, including Paper wasps and German wasps (as pictured above). At times I've dealt with this by engaging in combat with the creatures, and risking life and limb (or at least getting mildly stung) by going after them with a pair of scissors. But a more effective way is to set up a wasp trap, or if possible track down their nest and kill them using Blitzem Wasp Killer.
An all too common problem that many people face is running out of plants for the caterpillars to eat.
As the larvae get larger they can eat a surprising amount, and if you're not careful they will soon munch till you're out of plant. This is fine earlier in the season when swan plants are still available, but later on this can become a problem.
To solve this I'd encourage being discerning, and removing some of the eggs to ensure you don't end up with too many on one plant. It may also be worth trying to get some plants well established so that they'll provide masses of food in future years.
Due to differing levels of toxicity in different plants, problems can occur when you move caterpillars off one plant and onto another. In general it's best to let caterpillars make their own way onto new plants by placing them next to each other.
You can also lessen the shock by ensuring plants are well watered so that any imbalance of cardenolides is diluted.
Issues affecting Swan Plants
While the cardenolides present in the plant stop most pest species from bothering them, there are some aphids that regular infest the plant. Pesticides could be used to kill these little sap suckers, however these will also kill the caterpillars. As a result most gardeners resort to manual methods of control, either spraying them off with soapy water or squishing them on the plants.
Helping mature Monarchs
Butterflies are nectar feeders, and to ensure that your garden is full of these delightful creatures it's worth making sure that you have a wide array of flowers for them to feed on. For best results plant a wide array of flowers. And as an added extra this is also likely to bring in other beneficial insects into your garden such as bees, hoverflies, and lacewings.
Plants great for Monarch Butterflies include: Swan Plants, Ageratum, Cleome, Coreopsis, Dianthus, Echinacea, Hebe, Hyssop, Lavender, Osteospermum, Salvia, Verbena, Viburnum, and Zinnia.