The Accidental Lepidopterist: Monarch Butterfly Edition

UPDATED in 2025 with MORE PICS!

Freshly laid Monarch butterfly eggs are greenish/white. This cream/yellow one is probably about 3 days old.

Mid-August and my garden is a sandy strip of nothing-going-on. We've had weeks of 90s and oppressive humidity, and the stubs of golden alexander and parsley left by the Swallowtails are struggling to grow back. Yet I keep finding fresh eggs and caterpillars on them! Off to the nursery we went to find host plants. The herbs were wiped out so I headed for the clearance tables hoping to get lucky. There was nothing for Swallowtails but I found a table full of Tropical Milkweed (Asclepias curassavica) for $2.09. It was Buy2 Get1 but A.curassavica isn't native. Virginia put the VA in inVAsive so I picked a small 2 1/2" pot that, once home, totally surprised me with two Monarch butterfly eggs. I scrambled online to learn as much as I could, as fast as I could. A monarch butterfly egg hatches in 3-5 days, the shorter time with warmer temperatures, so the clock was ticking.

When mature, the egg doesn't turn solid black like a swallowtail's. Only the tip, the head of the larva, does (unless it's been parasitized by Trichogramma wasps). I think the freckles are what will eventually become tentacles.

The first thing I learned was that eggs laid after mid-August comprise the 5th generation of the year, the "super generation." It's the one that makes the incredible journey southward, traveling hundreds or even thousands of miles to overwintering grounds. Recently listed as endangered, I felt doubly pressured to ensure their survival.* 

I hope this helps you if you're in the same time crunch!

First meal: its eggshell (chorion).

Day 1 as caterpillars. I have to say, raising Monarchs is very different from raising Black Swallowtails. The method is the same: feed them their host plant, enable them to pupate, release a butterfly. But the experience is at a much faster pace and the details — the clues that tell you what to do next — are all different. 

To begin, newly hatched Monarch caterpillars are impossibly small, and it's frustrating trying to see if anything is happening. Turns out it isn't much, and they are completely boring at first. 

While black swallowtail caterpillars are almost as small, they offer a lot more opportunity to be found, probably because their survival strategy employs a little bird poop mimicry. You'll find them on leaf stems, topside of leaves, underside, on the flowers… and you can start each day with a little game of Where's Waldo. Monarch caterpillars, with no camouflaging strategy, have to be more discreet so spend almost all their time hiding on the bottom side of leaves.

Do you see both Monarch caterpillars? Click/tap the photo and scan the enlargement for a black head and pale green body.

Day 3 as caterpillars. First molt! They'll go through 5 just like swallowtails do. New black stripes make them a little easier to find, but I still needed a magnifying glass to find them. That's how I noticed little brown spots on the undersides of the leaves. Rust is a fungal plant disease that is host-specific (won't jump to other plants) and doesn't harm the caterpillars. It is less of a problem for plants when moisture is managed properly. Nurseries tend to both crowd and overwater plants, so hopefully this issue resolves itself especially now that it's in my kitchen.

I'm fairly certain the nursery mislabeled the plant I bought. The plant tag showed bi-color blossoms, but with fully orange blossoms and fine hairs on the small leaves and stems (visible in the macrophotos), this narrow-leafed milkweed is most likely Butterfly Milkweed (Ascelpias tuberosa). Native to eastern and southwestern North America, now I wish I had bought three.

An example of their skeletonizing method of eating. Click/tap the photo for an enlarged version. You'll be able to see the black nubs that will become the front tentacles.

Swallowtails neatly eat entire leaves and stems but early instar Monarch caterpillars need to avoid releasing the sticky white sap milkweed is known for. At their size it can glue their mouth parts shut, so they don't touch the leaf veins. They eat only the soft sections in between, leaving the plant looking a mess. I'm the relentless deadheader and weeder kind of gardener, so I'm having to learn to accept imperfection as perfection. 

Day 5 as caterpillars. All instars have multiple looks; the photo above and below are both 2nd instars! A Field Guide to Monarch Caterpillars (Danausplexippus) by Karen Oberhauser and Kristen Kuda is a terrific reference to determine which instar your caterpillar is.

A 2nd instar monarch caterpillar has two triangular spots behind the head. It's beginning to get yellow stripes.

 Day 6 as caterpillars. Third instar! With bright yellow stripes and prominent front and rear tentacle nubs, they're finally starting to look like Monarch caterpillars. This is a rapid growth stage that's easy to see.

Half a centimeter in the morning.

Doubled in length in one day!

Day 7: Third instars are less wasteful but still won't eat the central leaf vein. One site I referenced said they will snip the central vein to stop the flow of sap. Then they can eat all of the leaf after the snip.

Rather than skeletonizing, week-old caterpillars eat more leaf but not the midrib.

Day 8: Through the 3rd instar, my little $2 plant seemed plentiful for both caterpillars. But now they're eating full leaves including the midrib, which channels Milkweed sap. Eating leaves down to a nub, I began to really wish I'd bought three plants.

Just like Instagram, I'm experiencing upside down posting with Blogger. 🤷🏽

If you're desperate, older caterpillars, 4th or 5th instars, can eat slices of cucumber, zucchini, or butternut squash. You can also offer watermelon rind but feed them these alternatives only in a pinch. Pesticides will kill larvae so choose organic produce, and peel off anything that might be waxed.

A 4th instar caterpillar looks like a big juicy meal to predators, so now is a good time to load up on the sap. It's full of the toxins that make Monarchs mildly poisonous. Several sources said a single caterpillar eats an entire plant so I did the newbie panic thing of driving from nursery to nursery looking for milkweed plants, only to find none. Or a sad excuse for a plant, merely sticks and leaf remnants complete with more eggs or caterpillars. Already the accidental lepidopterist, I didn't need to buy more problems; I just needed food.

While late instar caterpillars can eat alternative foods, they'll render the caterpillars non-toxic to predators. In a process called aposematism, a predator learns to associate a warning signal, such as bright colors, with a bad experience and avoids all similarly-marked prey in the future. So it's important to feed your Monarchs milkweed only, for the protection of future generations.

Day 10:

A monarch caterpillar spends 3 to 5 days in its 5th instar, the shorter time with warmer temperature.

Day 13: As it turned out, I panicked for nothing. They abruptly stopped eating and kept walking off every leaf I offered. Monarch caterpillars do not do a purge, the telltale sign that a Swallowtail is ready to pupate. I had to take the refusal to eat as the sign and left them to do their thing, whatever it might be. After a few hours, they'd taken the j-formation side-by-side.

Hanging in J-formation, opposite to Swallowtails which suspend themselves head up, feet down.

Day 14:

Fifth instar Monarch caterpillar, preparing for its final molt.

Like the Swallowtail, they spend a full day in the pre-pupal position, not moving, and there are indicators that the final molt is imminent. When you see the caterpillar straightening out and tentacles go limp, it is ready to begin the final molt to chrysalis.

Dorsal view of the final molt to become a monarch chrysalis.

Day 15: A monarch can stay in its chrysalis for up to 15 days! Less time in warm temperatures. Here's a chart that illustrates the difference 10°F makes.

 

1-day-old chrysalis, wing veins already visible.

Day 22: The evening of their 7th day as chrysalides, they turned really dark. I am beginning to think all butterflies time it so they eclose early in the morning, to warm as the sun rises. A few hours in the sun's warmth helps their wings dry and harden.

Late night after 7 days as chrysalides, the famous orange and black wings clearly visible.

Day 23: As with our Swallowtails, we awoke to find an already eclosed butterfly clinging to it's empty chrysalis, its sibling ready to burst out of its own.

Good morning 8-day old monarch chrysalis and brand new butterfly!

I don't know if it is just the migratory generation that does this because they need extra-strong flight muscles for the journey to Mexico, but ours beat their wings pretty regularly and slowly, giving us ample opportunity to determine their sex. These are both males.

Monarch wings are translucent. The stripes visible when the wings are spread open (the dorsal side) are the same as those when their wings are folded (the ventral side). This is different from swallowtails, whose wing spots in open and closed positions are different, and you can only tell the sex when they're open.

The wings being translucent surprised me.

The outlook was for rain (as it often is here) so we held them overnight. In the morning, they could see the outdoors just on the other side of the window and were eager to get out. So eager that there was no placing them on a flower for a beauty shot, like I do with our Swallowtails. The instant we brought the hamper out, they flew out the opening, up into the forest canopy, and thus began their incredible journey to Mexico.

*The International Union for the Conservation of Nature added the migratory monarch butterfly just this summer to its Red List of threatened species and categorized it as "endangered." I find it interesting that the migratory monarch is considered a subspecies of the monarch butterfly (Danaus plexippus) and that the IUCN was specific about this, the last generation born each year. Regardless, endangered is two steps from extinct. We can't let this happen! For the migratory generation that will travel about 3,000 miles, we'll be planting summer- and long-blooming nectar plants like Lantana, Mexican Torch, and Zinnias. By this time next year, we hope to have transformed our strip of sand into a Monarch Waystation. For regenerative generations, those that fly north toward Canada in the spring, planting nectar plants in addition to milkweed is key to saving the species. It is the only plant monarchs will lay their eggs and the only food their caterpillars will eat (cucurbits notwithstanding).

A side note on milkweed aphids. Leave them on your plants! You'll offer predacious ladybugs, spiders, and ants something to eat other instead of your monarch eggs and larvae. https://pmc.ncbi.nlm.nih.gov/articles/PMC8234420/