Next up in our monarch mini-series, we take a look at the caterpillar stage of monarch life. First, we’ll take a look at the basics of caterpillar life. Then we’ll look a little deeper at 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.
Monarch Butterfly Egg Laying and Hatching
If you have swan plan, with any luck, you’ll soon have monarch eggs in your garden. After a few days, those little eggs will hatch into tiny caterpillars and begin a voracious cycle of eating and pooping. Since the eggs are often on the underside of the leaves, look for very small holes appearing on the leaves of your swan plants. Take a peek at the underside. Chances are good that there is a wee little hungry hatchling nibbling below. Monarch caterpillars nibble their way out of the shell, often eating it completely, and then keep straight on eating until they pupate.
Eggs that Fail to Hatch
Some eggs may not hatch. These may be unfertilised, have succumbed to unfavourable environmental conditions, been laid carrying a disease, or have been attached by a predator/parasite. Search your local monarch resources for risks and identification characteristics. If you suspect one of the latter, remove the egg and leaf or leaf section for disposal to reduce spread.
Very Hungry Caterpillars
Stocking the Caterpillar Buffet
The caterpillar stage of monarch life is entirely devoted to munching on swan plant (milkweed). Keep you plants clean, healthy, well-watered, and spray-free to ensure the milkweed is safe and yummy. 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 this by removing butterfly access to the swan plants after sufficient laying or removing excess eggs. Others let nature take its course and rely on environmental factors and predators to reduce numbers. We currently use separate plantings and partial access restriction to help manage our food supply, when necessary.
Watching Caterpillars Eat and Grow
Watching the 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.
Looking for caterpillars on your plants? After their wee little baby nibbles near their hatching point as noted above, small 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 below, 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 above, 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 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. In preparation for molting, the caterpillar uses its silk to secure the current skin in-situ. When ready, the caterpillar then walks out wearing the new skin beneath. The newly exposed skin is soft, and the caterpillar is particularly vulnerable at this stage. When ready, they often eat the skin (waste not, want not!) and then carry on munching milkweed.
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.