This year, our swan plants have grown, and they were very attractive to the monarch butterflies which pass through our yard, so much so that the monarch larvae (caterpillars) devastated our two swan plants. It was fascinating watching their life cycle.
Swan plants are a type of milkweed, and milkweed is the favourite (some say, only) food source for the monarch butterfly caterpillars. There are very few other plants that can sustain the caterpillars, especially pumpkins, but milkweed has a special chemical that the monarch needs to metamorphose from caterpillar into a butterfly.
When the monarch butterfly lays its egg, it is opaque and creamy yellow. (I watched the mother monarch lay this egg and then immediately photographed the egg. I didn’t want to get too close to the mother for fear she would depart, so I didn’t photograph her.)
After three or four days, when the monarch butterfly egg is ready to hatch, it turns more transparent, and you can then see the larva (caterpillar) inside.
When the monarch butterfly caterpillar/larva first hatches, it is opaque-white with a large black head. Its first meal is its own eggshell. Shortly, however, it gains a bit more colour, though not much during its first instar (caterpillar stage).
All the monarch larvae (caterpillars) do during their two to four week life is eat and grow, eat and grow, eat and grow. The entire life of a caterpillar is two to four weeks, depending on the temperature. During colder weather, they grow more slowly.
During the second and third instars, the monarch caterpillar has its famous black, white, and yellow stripes.
During the fourth and fifth instars, the caterpillar has longer antennae.
The fifth instar will attach its legs to a stem or leaf and weave a cocoon around itself.
The monarch will then remain in the cocoon (chrysalis) for approximately ten days before emerging as a full-grown monarch butterfly.
This is a female, since she has the thicker black lines in her wings and does not have the two black dots on her hind wing that the males have.
After the leaves grew back on our swan plants, I am sure she laid some of her 300 to 400 eggs on our plants, though the next generation didn’t have as many caterpillars and so didn’t devastate our swan plants like the first generation did.
We had so many monarch butterfly caterpillars on our two swan plants that they literally devastated our plants, removing all the leaves and eating many stems and seedpods. Unfortunately, since I didn’t realise how much each caterpillar will eat, I simply watched in awe of the growing caterpillars.
It wasn’t until it was too late that I realised that they were going to run out of food before they all grew large enough to metamorphise into butterflies. We ended up having only two cocoons on one of our swan plants, and none on the other. All the rest of the caterpillars died of starvation.
Here in New Zealand, there are four generations of monarch butterfly each summer. The monarch butterflies will live two to six weeks during the summer, but then the fourth generation will live the entire winter until the next spring, at which time they will lays eggs and begin the cycle all over again.
We harvested some of the seeds from our swan plants this year and are beginning to grow seedlings that we can then plant around our place. I’m also going to try to grow swan plants from cuttings that I will take from our two original plants. The monarch butterflies are a beautiful sight, especially when there are several of them flapping around our yard.
When I first saw the monarch butterfly larvae growing on our swan plants, I wondered how far they would migrate for the winter. It turns out that New Zealand monarch butterflies don’t migrate at all. They spend their entire lives here.