Monarch Butterfly: Vibrant Fliers at Risk

With their tiger coloring and 4-inch wingspans, the monarch spends at least part of its life in every state of the lower 48. Seven states, from Texas to Idaho to Vermont, have designated the monarch the state insect.

Monarchs carry on one of the most spectacular seasonal migrations of any creature on earth. The population east of the Rockies overwinters in small isolated "islands" of oyamel fir trees in the mountains of central Mexico. In the spring, these individuals only get as far as the southern U.S. before they breed and die. Their descendants continue the migration cycle.

Global Warming Threats

Climate change poses a two-barreled threat to these beautiful travelers, affecting both their wintering grounds and summer breeding grounds.

In the high altitude conifer forests of central Mexico where they spend the winter, wetter, colder conditions are predicted over next 50 years. Rain followed by freezing temperatures can be lethal to overwintering monarchs.

The hotter, drier summer conditions predicted for eastern U.S. and Canada could shift suitable habitats northward, possibly extending migration distances. High temperatures or drought could affect food resources, reproductive success and adult survival. It's unclear whether the range of the larval monarch's host plant, milkweed, will shift with the butterfly's range.

Wider Implications

The monarch's awe-inspiring migration story is a wonder of nature. Monarchs may not be the proficient pollinators that bees are, but because they migrate over vast distance, they pollinate plants across the country.

Other Butterflies at Risk

Many butterfly species are particularly vulnerable to global warming because of their complex life cycles and sensitivity to climate. They may be fatally affected by heavy precipitation, drought, or “false springs” that result in early flights followed by winter storms. And they tend to rely on specific food sources that can be impacted by climate change.

Some, like California's Edith's checkerspot butterfly, are already exhibiting range shifts northward or moving upslope in response to climate change. Others, like the Uncompahgre fritillary, a butterfly species that inhabits snow willow patches above 13,000 ft in southwestern Colorado, will have no higher places to go as its glacier-like environment warms.

Sources

• http://www.sciencedaily.com/releases/2003/11/031111071802.htm
• http://www.ncbi.nlm.nih.gov/pubmed/18284764
• http://www.xerces.org/wp-content/uploads/2008/09/boloria_acrocnema.pdf
• http://www.fws.gov/midwest/Endangered/insects/kbb/index.html

Posted: 11-Jun-2009; Updated: 04-Jun-2009