March 27, 2013—A couple of weeks ago news broke that the number of monarch butterflies overwintering in Mexico had plummeted 59 percent this year. The common wisdom put blame on three factors: past deforestation of the Mexican preserves, a hot, dry summer in the U.S. and Canada, and the extensive use of herbicides—especially in the agricultural Midwest—that wipe out milkweed, the only thing monarch larvae eat.
This looked like bad news, of course. But I figured it was bad news that didn’t really apply to us here in California. The monarchs that winter in Mexico belong to a population that spends the rest of its life cycle east of the Rockies. I figured our monarchs—the ones that winter at Natural Bridges State Beach, Pacific Grove and about 200 other sites along the California coast and spend their life cycles west of the Rockies—were better off, the West being more enlightened and all.
So much for that. As San Jose State University biologist John Dayton told blogger Laura Tangley, the California winter monarch population is down 90 percent from the mid-1990s. At Natural Bridges, a 1997 count of 120,000 wintering butterflies has tapered off to an anemic 1,000-2,000. Tangley describes going there to find the monarchs she remembered from her UCSC days, only to be advised to try Lighthouse Field instead (she did see a few hundred at Lighthouse Field).
So what’s the problem? Some think the coastal overwintering sites aren’t well enough protected. In Pacific Grove, a.k.a. Butterfly Town, U.S.A., for example, a naive (some would say idiotic, but why split hairs) decision to prune the eucalyptus trees in 2009 basically made it so no monarchs showed up that year at all.
Then there’s the milkweed issue. A 2010 CNET article on the coastal monarch population blames the crop for which the West has become infamous: houses.
Milkweed, author Daniel Terdiman writes, is “gradually disappearing in crucial parts of California as housing subdivisions replace the orchards, meadows, and vacant lots where the plant once proliferated, and as more efficient farming methods have allowed people to grow crops at the margins of their properties, places where milkweed used to thrive.”
There is something we can do, then: plant milkweed. And convince your friends throughout the interior West to do it too. And maybe especially work on your relatives in the Midwest. A group called Monarch Watch sells Waystation Seed Kits ($16) containing four or five types of milkweed seed as well as seed for monarch-friendly nectar producers. Monarch Watch also has this handy guide to butterfly-friendly bushes.
It's probably not a cure-all. But it's a lot better than doing nothing.