25 02 2014 Monarch Butterfly Migration
Are we witnessing the end of the monarch butterfly's spectacular mass migration? The answer could be 'yes' unless something is done to restrict the use of the Roundup herbicide. Image: farflungphotos, Flickr

This week, Natural Resources Defense Council (NRDC) filed a petition to the United States’ Environmental Protection Agency to reexamine the use of common weed-killer glyphosate before it destroys one of the marvels of the natural world.

Each year, up to 300 million orange and black monarch butterflies migrate to Mexico to escape the harsh winters of Canada and the eastern United States. The sight is unlike anything else in the world (visual proof here - it's six minutes of pure beauty!). But the species is now in serious danger.

You see, because each monarch lives only a few weeks in the summer, it takes several generations of butterflies to make the round-trip from Mexico to Canada and back. Only every fifth generation reaches Mexico, where they hibernate for the winter and mate in the springtime. They then begin the long journey home, laying their eggs along the way, because they will die before reaching their destination. The eggs hatch and the larvae grow into new butterflies that continue the magical journey in a pattern unbroken for millions of generations. 

But this year, a count in Mexico reveals the lowest numbers of monarchs since studies began in 1993, leading experts to announce that the insects’ annual migration is in danger of disappearing.

“The eggs hatch and the larvae grow into new butterflies that continue the magical journey in a pattern unbroken for millions of generations.”

One reason for this is the increasing use of glyphosate, commonly known as Roundup, now the most widely used herbicide in the US. Roundup transformed American farming by killing the weeds and grasses that compete with commercial crops, but it also kills milkweed, the native American plant that is the sole source of food for monarch butterfly larvae. With nothing to eat, the larvae cannot survive to make the next leg of the migration. While many herbicides can kill milkweed, it is the current widespread application of glyphosate that has "contributed to significant habitat loss along monarch migratory paths," the NRDC’s petition says.

Since the glyphosate rules were last updated in 1993, its use has soared tenfold to 182 million pounds a year, following the introduction and rapid spread of 'Roundup Ready' corn and soybeans that now dominate Midwest farms. These crops are genetically modified to resist the weed-killer, and more herbicide-tolerant crops are in the pipeline, cautions the NRDC, raising new threats to monarch habitat.

The EPA is scheduled to complete a new review of glyphosate rules next year, but – given the rapid decline in monarch numbers – the NRDC urges the EPA to take immediate steps to review and restrict use of the substance, as well as other weed-killers that may be equally bad for monarchs and could pose health risks.

"[The loss of these] beautiful and unique creatures ... signals a warning about the unintended consequences of our industrial agricultural practices," says Sylvia Fallon, a senior scientist and blogger with the NRDC. "We need to act quickly to ensure that future generations will also be able to experience the wonder of the monarch’s migration."

How you can help:

Kansas-based non-profit educational outreach programme Monarch Watch offers free milkweed plugs for schools and organisations to help rehabilitate monarch habitats. To see if you qualify, click here.

Where are the monarchs?

For a gripping fictionalised insight into the consequences of the changing migration patterns of monarch butterflies, read Barbara Kingsolver’s 2012 bestseller Flight Behavior.

Top header image: USFS Region 5, Flickr