Hosting Monarch Caterpillars in Your Garden

Monarch caterpillar eating swan plant (milkweed)

Next up in our monarch mini-series, we take a look at the caterpillar stage of the monarch life cycle.  First up, we’ll take a look at the basics of monarch caterpillar development. Then we’ll zoom in a little deeper on specific aspects of caterpillar hosting, including housekeeping, movement, and predators. These can help monarch caterpillars have a greater chance of surviving to form a healthy chrysalis and become a butterfly. 

Green in Real Life blog space bar small right flower

Monarch Butterfly Egg Laying and Hatching

If you’re growing swan plants (milkweed), with any luck, you’ll soon have monarch eggs in your garden. After a few days, those little eggs will hatch into tiny monarch caterpillars and begin a voracious cycle of eating, pooping, and growing. 

Since the monarch eggs are often laid on the underside of the swan plant leaves, keep an eye out for very small holes appearing on the leaves of your swan plants. Spot some? Take a peek at the underside of the leaf. Chances are good that there is a wee little hungry hatchling, like this one, nibbling below. Monarch caterpillars nibble their way out of the shell, often eating it completely, and then keep straight on eating until they pupate. 

Newly hatched monarch caterpillar on swan plant (milkweed) leaf

Eggs that Fail to Hatch

Not everything goes smoothly in nature, and some eggs may not hatch. These may be unfertilised, have succumbed to unfavourable environmental conditions, been laid carrying a disease, or have been attacked by a predator/parasite.

Worried that it might be a monarch health issue? Search your local monarch resources for risks and identification characteristics. If you suspect parasites or diseases, you can remove the egg and leaf (or leaf section) for disposal to reduce spread.

Paper wasp hunting monarch caterpillars

Very Hungry Caterpillars

Stocking the Caterpillar Buffet

The caterpillar stage of monarch life is entirely devoted to munching on swan plant (milkweed). Keep your swan plant buffet clean, healthy, well-watered, and spray-free to ensure the leaves stay safe and yummy for your developing caterpillar guests.  

I can’t stress enough that these guys eat a lot! It’s essential that you have enough swan plant to feed your caterpillars. It’s better to have a swan plant oversupply, if possible.  

Some people choose to manage supply vs. demand by removing butterfly access to the swan plants after sufficient laying or by removing excess eggs once they reach capacity. Others just plant and then let nature take its course, allowing environmental factors, predators, or the hunger games to play out. We currently use separate plantings and partial access restriction to help manage our food supply, when necessary. 

Monarch caterpillars eating milkweed (swan plants)

Watching Monarch Caterpillars Eat and Grow

Watching the monarch caterpillars munch away is one of the best parts of having swan plants in the garden. I’ve also been amazed at how fast and far they can move – especially the big caterpillars. 

Searching for Caterpillars on Swan Plants

After their wee little baby nibbles near their hatching point, as noted above, small monarch caterpillars can often be found in the fine new growth at leaf-tips, which offers good natural concealment from predators.

Big caterpillars are far easier to spot, like the feasting masses in the photo above, but they also have a few sneaky tricks. Monarch caterpillars sometimes dangle on the underside of a droopy looking leaf as shown in the collage below, munching their way from the tip back to the stem. The droop isn’t solely from the weight of the big caterpillars (or “fatties” as I like to call them at this stage). The clever caterpillars often nibble a notch at the base of the leaf. This reduces the amount of sticky sap making it a better/safer food, especially in hot weather and (coincidence or cleverness?) creates a semi-concealed dining position on the plant for predator avoidance.

Monarch caterpillar nibbling wan plant (milkweed) to dangle underneath leaf

Monarch Caterpillar Growth and Development

Munching and Molting

The rapidly eating and growing caterpillars will molt (shed their exoskeleton) as they become too large for their old skins. We talk more about the growth cycle stages below. 

In preparation for molting, the caterpillar uses its silk to secure the current skin in-situ. When ready, the caterpillar walks out wearing the new skin beneath. The newly exposed skin is soft, and the caterpillar is particularly vulnerable at this stage. Afterwards, they sometimes eat the skin (waste not, want not!) and then carry on munching milkweed. 

Monarch caterpillar resting on leaf next to molted skin

Instar Growth Stages

Molting is the process by which a caterpillar progresses between main growth stages, referred to as instars. There are five instars of monarch caterpillar, each increasing in size and changing slightly in appearance from the previous. 

Each stage of development only takes a matter of days and, all totalled, a monarch caterpillar usually goes from egg to chrysalis in under two weeks.

Mature Instar Caterpillars

When a mature 5th instar caterpillar is ready to pupate, it will often journey away from the milkweed (or climb if enclosed) and look for a suitable place to transition into chrysalis, which we’ll look at in detail in the next stage of the mini-series. 

But first, stay tuned for a closer look at some of the detailed aspects of hosting healthy happy caterpillars. Here are some deeper dives on supporting monarch caterpillars:

Hosting Monarch Caterpillars in Your Garden

You might also enjoy: