Why are caterpillars disappearing from my milkweed patch?

There are a number of potential reasons for this. If disappearing caterpillars are 5th instar caterpillars, odds are they moved away from your milkweeds to find a safe place to form their chrysalis (they typically do not pupate on milkweed plants). If earlier instars or eggs are disappearing, a more likely culprit is a monarch predator. You can read more about natural enemies on our website. Researchers agree that less than 10% (with some studies as low as 2%) of monarch eggs reach adulthood.