What are monarch butterflies doing in my garden

Monarch (Danaus plexippus).


What are monarch butterflies doing in my garden. No, I don’t mean what right do they have to be in my garden. I mean, literally, what is it that they are doing.

We all know monarchs are migratory. Adult monarchs from this area spend winters in Mexico. It’s obvious from the photo above that this monarch likes zinnias for nectaring. I’ve never seen a monarch anywhere near a milkweed plant. So why is it important for me, in New Jersey, to provide them with milkweed, their larval food plant. I need a monarch education.

My first sighting of a monarch this summer was on September 13, captured in the photo above. Isn’t it wonderful how nature pairs up the most extraordinary colors, and they always look beautiful together. At least to me.

Gochfeld and Burger, in Butterflies of New Jersey, report the first arrival of monarchs in New Jersey in mid-May, with a first brood in late June, and 2 or 3 later broods throughout the summer. Southward migration starts in late August, peaks in September, but continues through October, with a few monarchs still moving through the state in early November. NABA North Jersey Butterfly Club website gives extreme dates for North Jersey monarchs as 4/15 to 11/29.

So, the monarchs in my garden this September are Mexico bound, it appears. So, again, why am I planting milkweed, their larval food plant. Maybe I missed some early monarchs. Maybe, these September monarchs hatched from eggs laid on the milkweeds in my garden; as caterpillars, maybe they went through their 5 instars, or stages between molts; formed pupa; and metamorphosed into adult butterflies right here, right under my unobservant nose.

The butterfly in the photos above, taken on September 20, is a male. The NABA Club website explains that males have small black scent patches along inner hindwing veins, 1 of which can be seen in the photos above. There were 2 monarchs in the garden on September 20, but I got photos of only this one. Look at his left wing. There’s something wrong with it. Still, he seemed to fly ok. But will he make it to Mexico. We’ll never know.


Butterflies in New Jersey lists zinnias as attractive to swallowtails. I agree. In my observations, also attractive to great spangled fritillaries and to monarchs, plus multitudes of bees, wasps, and other insects. But Butterflies in New Jersey makes an important distinction in zinnias. The “double” varieties that have been bred for their showy looks have little or no nectar. So, look for the old-fashioned zinnia varieties that have the small, yellow central heads where nectar is produced. Good thing to know.


According to the Monarch Watch website, butterfly sensory systems are very different from ours. They see ultraviolet light and hear ultrasound, for example. They have chemoreceptors, like tastebuds in humans, scattered across their bodies. Their antennae are densely covered with chemoreceptors, which they use for many things. For mating, to discover their host plants, and to sense nectar sources. When butterflies sense nectar through chemoreceptors on legs and antennae, they extend their proboscis to feed on the honey-smelling, sugar-tasting nectar. No wonder this monarch looks somewhat obsessive while nectaring. That’s good stuff.


Also according to the Monarch Watch website, monarch butterflies deter predation by vertebrates, such as birds, by sequestering poisonous cardenolides, or cardiac glycosides, from the milkweed they eat as caterpillars. A predator may bite the monarch, taste the poison, and release the butterfly without killing it. Perhaps that’s what happened to this monarch. As an additional deterrent, the bright coloration of monarchs is a warning to predators that poisonous chemicals are present. Wow. And we like to think those beautiful colors are there for our enjoyment.

So milkweeds contain poisonous chemicals. I know that as a child I developed some sort of allergy to common milkweed found growing in pastures. But my cousins seemed immune to whatever caused my skin rash, or whatever it was. My memory is sketchy, and I am no longer able to ask those people who might be able to enlighten my memory. One of the drawbacks of growing old.

I planted 3 types of milkweed in the gardens. Butterfly weed (Asclepias tuberosa).


Common milkweed (Asclepias syriaca).


Red milkweed, or swamp milkweed (Asclepias incarnata).


Important to remember that milkweed is a weed. I accidentally hit the stalk of a milkweed that was past flowering with a weed whacker, and the explosion of seed pods was startling and impressive, to say the least. Butterflies in New Jersey reports that milkweed seeds have a poor germination rate. When I saw all those cottony seedpods floating in the wind, I was somewhat comforted by the idea that perhaps they would not all germinate. Weeds. But monarchs need them. And they are attractive. Weeds or wildflowers. It’s always a tradeoff in a small garden area.


This is a photo of what remains of the milkweed after the weed whacker incident. The backdrop is a jungle of Matt’s wild cherry tomatoes. So much remarkable wildness in a suburban garden.

But I still haven’t answered the question of why I’m providing milkweed to monarchs in New Jersey. So far, I’ve watched a couple of monarchs nectaring at zinnias in September, preparing for their southward migration. Again using Monarch Watch website as my source of information, I learn that adult summer generation monarchs live from 2 to 5 weeks, as compared to the fall migratory monarchs, who live 8 to 9 months. Wow.

Summer generation monarchs go from egg to adult in 30 days. Female monarchs lay 100-300 individual eggs on the underside of the top leaves of milkweed plants. The eggs hatch after 4 days. The larva, or caterpillars, go through 5 instars, or intervals between molts. Molting being the shedding of skin as the caterpillars grow in size. The caterpillar stages last 10-14 days. After which the pupa or chrysalis is formed for a duration of 10-14 days. The adult monarch emerges and the metamorphosis is complete. So, my milkweed is important for summer generation monarchs. In New Jersey, this would be from mid-May through late August.

I must suspend my disbelief and nurture the milkweed in the hope of finding it useful to monarchs. Perhaps the summer generation monarchs have not discovered my garden. Perhaps they were here during the summer but I didn’t happen to see them. My monarch plan, which is really a butterfly plan, is to provide the best larval food plants and nectaring plants for New Jersey butterflies, to continue to learn about them, and to be more observant. At least now I have a better idea of what monarchs are doing in my garden.










One Comment on “What are monarch butterflies doing in my garden

  1. Pingback: Home-grown monarchs and milkweed – daysingarden

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