Q. I planted a pollinator garden several years ago and specifically included different types of butterfly weed (Asclepias spp.) for monarch butterfly larvae. But I haven't had any takers this year. Where are they?
A. You are not alone. Monarch-loving residents of the northeastern United States have been asking the same thing. A number of factors have conspired to reduce the monarch population to record lows this year.
One of the biggest issues is habitat loss, both in the U.S. and in their overwintering grounds in Mexico. Logging in Mexico is shrinking monarch habitat there. Loss of farmland fields and natural areas to residential and commercial development in the U.S. has reduced habitat for milkweed because manicured lawns and ornamental beds (not to mention pavement) supplant native species. Also, the widespread use of herbicide-resistant soybeans and corn in modern agriculture has increased the use of nonselective herbicides that effectively eliminate butterfly-friendly plant species that may have survived applications of other herbicides.
But loss of habitat is not the only problem. Eastern monarchs pass through Texas on their way to and from Mexico, and Texas is in the grip of a multiyear drought. Fifty-four percent of rangeland and pastures in the state have been rated as "poor or very poor," and some parts have been in "extreme drought" (as rated by the U.S. Drought Monitor) since 2010. The drought and periodic wildfires have severely reduced milkweed populations in Texas. Given that milkweed is the only larval food for monarchs, less milkweed means fewer butterflies.
Monarch migration is a carefully choreographed dance that requires the coordination of three or four generations. Generation 4 adults are those we see (or should see) at this time of year and are those that make the perilous journey from Western Pennsylvania to Mexico, where they overwinter. They are the longest-lived generation, with a typical lifespan of six to eight months. Although monarchs travel to their winter grounds in a single generation, it takes three or four generations for them to return to the northern United States and Canada the following year, with each generation pushing farther north. These generations have much shorter life spans than generation 4, perhaps four to six weeks. Monarchs are dependent on finding sufficient milkweed along the way. When drought, agriculture and/or development have eliminated it, that may be as far north as they can go that year.
Despite the fact that the 2012-13 overwintering monarch population in Mexico was 59 percent smaller than the year before, butterfly experts are not suggesting they are headed for extinction. Like most insects, monarchs reproduce rapidly and their population can recover from such crashes. Planting pollinator gardens that include species of milkweed is one the best things humans can do to help.garden
Send questions to Sandy Feather by email at email@example.com or by regular mail c/o Penn State Extension, 400 N. Lexington Ave., Pittsburgh 15208. First Published October 11, 2013 8:00 PM