With fall on the way, we have been anxiously watching for monarch butterflies to return to the Central Coast of California. My heart rejoices every time I see one flutter by. It won’t be a mass migration as these butterflies travel solo at up to 200 miles a day. They are traveling from as far north as Canada and west of the Rocky Mountains, where they have spent the summer. When they arrive here on the Coast of California, it will have been four generations since they last overwintered here.
The Pismo Monarch Butterfly Grove on Highway One is located at the border of Grover Beach and Pismo Beach. For years it has been one of five locations in California that harbor more than 10,000 Monarchs during the winter. The last few years we have seen declining numbers, until 2021 when they were counted in the 22,000 range. We all have been riding that high for quite a few months but the future is uncertain.
In July of 2022, the International Union for Conservation of Nature (IUCN) re-classified the Monarchs as endangered. This new classification does not mean any legal or regulatory protections in California. The U.S. Fish and Wildlife Service has not changed the Monarch status from declining to endangered. In fact, Monarchs are not listed as threatened or endangered under the California Endangered Species Act.
What can be done to help Monarch butterfly populations? The overwhelming information is to provide them with food. Adult monarchs feed on nectar bearing flowers, so planting early and late season bloomers is beneficial. Milkweed (Asclepias spp.) is the only plant monarch caterpillars eat, and it’s where the adult butterflies lay their eggs. Without it, Monarchs simply could not exist. But beware, an invasive species called tropical milkweed (Asclepias curassavica) does more harm than good. The non-native plant is problematic because in our climate, it doesn’t die back and can trick the butterflies into not recognizing when it’s time to migrate. This perpetuates the spread of deadly parasites to the next year's generation of caterpillars.
So many of the problems plaguing the Monarch are out of our control but the most destructive element is pesticide and herbicide use. Many chemicals are used in the nursery industry to keep plants attractive on the store shelves. If the butterflies lay eggs on treated plants, their caterpillars will die after eating the leaves. Neonicotinoid pesticides are especially harmful. They can kill bees and adult butterflies that ingest the toxic pollen and nectar of treated plants. The substitution of insecticidal soaps, horticultural oils or Neem oil will lessen the problem. Ultimately rethinking the widespread use of pesticides is crucial to the future of our butterfly population.