Help to Avoid Monarch Extinction

Recent news reports have described a dramatic decrease in California’s population of Western Monarch butterflies. Thirty years ago, over 4.5 million of these beautiful flying insects migrated annually from Mexico to overwinter on the Pacific Coast, with huge, fascinating clusters at famous sites, including Pacific Grove and Natural Bridges State Beach. Their numbers have declined over the years: this year the count was under 30,000 individuals, 0.6% of the population’s historic size. Researchers had established 30,000 as the “quasi extinction threshold,” so coming under this threshold suggests that this species (Danaus plexippus plexippus) is approaching extinction.

Another, larger number of monarchs migrate from Mexico to the northern plains of the United States, so extinction is not imminent, but that population also has been shrinking in recent decades.

The causes of the decline in the monarch population begin with the loss of suitable habitat, defined as areas that include both milkweeds (Asclepias sp.) that Monarch caterpillars depend upon, and pollen plants that provide nutrition for the adults. Milkweed plants are too often deleted from the environment by agricultural pesticides, particularly glysophate (RoundUp), which is used to kill unwanted plants among commercial crops.

Other factors include pesticide use, climate change, and logging and development projects that degrade overwintering sites.

Gardeners can help rescue monarch butterflies back from the threat of extinction by growing milkweed plants in their gardens, with preference for locally native species of this plant. Fifteen species of milkweed are native to California. Nearby sources of seeds for native species include Pacific Coast Seed, in Livermore; Seedhunt, in Freedom; and S&S Seeds, in Carpenteria. For information on growing milkweed, download “Native Milkweed in California: Planting and Establishment.”

A related project for gardeners is to include pollen plants for the adult monarch butterflies. Useful advice for such a project is available in “California Coast: Monarch Nectar Plants,” available here.

Both of these publications are free downloads from the Xerces Society for Invertebrate Conservation.

Monarch butterfly on Milkweed pod. Photo by Edward K. Boggess, U.S. Fish & Wildlife Service Posted on Wikimedia Commons

The Xerces Society has also produced a five-step call to action for recovering the western monarch population. This plan emphasizes protection of overwintering and breeding habitats, protection from pesticides, and continuing research on western monarch recovery. In addition to actions in their own gardens, people concerned with threats to the monarch population could support large-scale initiatives that respond to the Society’s call to action.

Protecting the Western Monarch Butterfly from extinction has at least three broad objectives. One is for us all to enjoy the phenomenon of these beautiful creatures flitting about in our gardens. A second objective, oriented to the ecosystem, is to maintain these butterflies as food sources for birds, which we also appreciate and enjoy. Thirdly, Karen Oberhauser, director of The Monarch Butterfly Lab at the University of Minneapolis, advises that monarch butterflies are valuable subjects for ongoing studies of migration, species interaction, insect population dynamics, and insect reproduction.

We can strive to keep monarch butterflies in our environment, but we should also acknowledge the larger picture of the extinction of species. Before humans spread across the globe, species extinctions occurred for various reasons at a very slow rate. Human activity has increased the average rate of extinction by somewhere between 100 to 1,000 times the previous historical rate., and is accelerating

Today, according to Edward O. Wilson, distinguished American biologist, the science community estimates that Planet Earth has about 10 million living species, one of which is human people (Homo sapiens). About 20 percent of these species are known, and 80 percent are undiscovered. If the extinction of species by human activity continues to accelerate, E.O. Wilson says, we could eliminate more than half of all species by the end of this century.

We can slow this trend a little by working as individuals. Consider adding California native milkweed and pollen plants to your garden this year, to sustain the monarch butterflies.

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