Where Did the Caterpillars Go?

Yes, my learning about monarch caterpillars continues. This has definitely been a learn-on-the-fly (or learn-on-the-butterfly?) adventure. Clearly I knew very little about monarchs as I happily planted milkweed in my yard this summer.

Each morning I have checked on my caterpillars after turning on the sprinkler for my newly installed sod. Slowly over the last couple of days, my milkweed plants have become finely chewed, but the caterpillars were missing. I feared my efforts to help populate the world with more monarch butterflies had been a failure.

Then, while turning on the hose this morning, I found this one hanging from the siding of my house.

monarch caterpillar hanging from the siding on my house
Photo taken at 7:10 am on Wednesday, August 12, 2020

Here’s how far the caterpillar crawled to get there. I took the picture standing next to the milkweed.

picture showing the distance from milkweed to house
The distance from the butterfly plant to the house is about 12 yards

Just an aside, that’s my tri-colored corgi, Misha. His new nickname during this pandemic is Prozac because whenever anyone needs a quiet moment, Misha is there to cuddle. (And know my husband is a psychiatrist, so we respect what Prozac does for people who struggle with depression). Misha is also affectionately called Hoover, is in the vacuum cleaner. If you have ever co-existed with a corgi, you know they are food motivated to-the-max. Misha loves living with three parrots who find it fun to feed him.

My corgi and my parrot
Misha and Toby, a 32-year old Congo African Grey parrot

Back to the caterpillars. I had really thought the caterpillars would pupate on a plant. Shows how much I didn’t know. And that conclusion came from watching caterpillars in my younger daughter’s Montessori classroom pupate on the plants. But when the monarch caterpillars are in the wild, they act differently.

When monarchs are in their chrysalis, they are vulnerable to predation by wasps and flies. It’s important for caterpillars to find a spot that they feel secure from predators, as well as sheltered from wind and rain. Caterpillars do not usually pupate on their host milkweed plants. Instead, they move as far as 10 meters from their initial plant to a tree, another plant, or even the side of a house!


I went outside an hour after I took the picture above to measure the distance this caterpillar had crawled. Look what I found!

monarch chrysalis
Monarch chrysalis

As this chrysalis becomes fully developed, there will be gold dots along the top edge, like this.


Fred Urquhart first studied the gold spots on monarchs in the 1970s. He felt that the spots were involved in the distribution or formation wing scale coloration. However, the experiments that he did involved cauterizing the gold spots on the pupa, and it is possible that this process may have damaged the underlying tissue and affected the color patterns. Interestingly, all danaine butterflies (monarchs and their relatives) have metallic spots on them. A group of researchers in Germany did a careful study of the properties of these spots. They are not metallic (so they aren’t really gold), but the cells reflect light like metals do, giving them the appearance of being metallic. Other danaids have silver, copper, or gold spots.


Here are some hypotheses for the reasons that these butterflies have metallic-looking spots on their pupae:

Camouflage — they could reflect colors of the surroundings and break up the shape of the pupa; they might also look like dew droplets.

Warning coloration

Filtering particular wavelengths of light which might be harmful to the monarchs

They might not have any function but just be the result of something else in the cuticle of the insect.

Oxygen exchange


I know what you’re thinking. My daughter asked at breakfast.

Mark your calendars. Anywhere from 9-to-14 days from now (August 20 to August 26) the world might have one more monarch. Now where the other ones crawled off to, I have no idea!

But wow, isn’t nature amazing when we take time to watch it?

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