It is spring and our butterfly gardens are coming alive.
My landscape includes host plants for dozens of local species (that is nerd speak indicating that I have specific plants that butterflies lay eggs on). I spend hours outside searching for caterpillars and chasing adult butterflies. I know many of you can relate.
Maintaining a butterfly habitat is so rewarding and...sometimes frustrating.
I have been teaching about butterflies for over 10 years and one of the most common questions I get is, "Why Are My Caterpillars Disappearing?".
This is a question I have heard hundreds of times. As usual, in science, there are many possible explanations to this but we will go over the most likely reasons.
Typically, beginners find it rewarding to start this hobby by planting Milkweed. The new enthusiast finds Monarch eggs and then tiny caterpillars on the plant, usually on the underside of the leaf. In a few days the tiny babies have grown quite a bit and within about 10 days, they are chubby and about 2” long. Then they disappear.
Sometimes they disappear as smaller caterpillars too.
Butterflies are quirky. While some species will often form a chrysalis on their host plant, many will usually not (unless you have them in captivity). They are likely to wander off once their internal clock triggers the beginning stages of the transition to adulthood.
Monarchs (and other kinds too) will often crawl to what they perceive as a safe location, somewhere within about a 40’ radius from their host plant. In nature, larvae will only leave their host plant intentionally if they are completely full and finished eating, unless they are leaving for a temporary molt session. So, if your tiny caterpillars (under 2” long) are disappearing something else may be happening.
Another possible explanation for why caterpillars disappear is that the plant has no more leaves to eat. If their host plant happens to be a smaller sized plant, they are more likely to run out of edible foliage before they have collected enough nutrients to begin metamorphosis. Sometimes if they run out of food they will go into a chrysalis prematurely but will die of malnutrition. Other times they will wander off of the plant in search of more of the same species of host plant to finish off their juvenile diet requirements.
The trouble is, caterpillars have no navigation skills whatsoever. They have poor vision that can simply tell light from dark. They don’t have the advanced antennae that adults have. No GPS. Their only hope is that they stumble upon another host plant while aimlessly wandering in search of food.
Yes, this is somewhat sad, but in the wild this is not uncommon. When I see a “lost” smaller sized caterpillar in my yard I carefully place it back on its host plant.
A third possibility is cannibalism. Sometimes larger caterpillars unintentionally eat eggs or tiny caterpillars. If you are raising caterpillars inside, keep the two sizes separate.
A fourth explanation for why caterpillars disappear is bittersweet. Their role in nature is to be the bottom of the food chain. They are the bottom of the trophic-level system. This means that they are the food that supplies larger animals with food that supply still larger animals with food and on and on. I completely understand that as a butterfly parent this may upset you, but it is nature. It’s the Circle of Life (insert Lion King song).
Finally, they may simply be outsmarting you. They are often masters of disguise in one stage or another. Caterpillars can camouflage. Many species will pupate directly on their host plant in disguise. Some chrysalises look just like dead leaves. Some look like live leaves. The Giant Swallowtail chrysalis in the photo below looks like a broken twig. There is a chance you are missing them as they are right under your nose.
Butterfly Gardening is a fabulous hobby. I have dedicated years of my life to my own garden patch and to helping others, like you, create their own. But we must remember that we cannot override the natural systems that exist on this amazing and complex Earth.
There will be victory and there will be loss. Enjoy the flow and the mystery that life is.
This post is a modified excerpt from my book Raising Monarch Butterflies: In Your Garden