Monarch Butterflies at Risk in N. America

B. McPherson

Let's make sure future generations have a chance to witness this.

For many N. Americans the return of the monarch butterflies is a sure sign that summer is here. These special butterflies with their cheery black and orange coloring are unique in their migratory habits. Because the monarchs are vulnerable to cold, they fly south in the autumn to winter in Mexico and California. They gather in the thousands in trees and enter a state of reduced metabolic activity, living on their fat reserves.

The epic journey of the monarchs is under siege.  In both the eastern and western populations, butterfly counts have plummeted in California and Mexico. The November 1997 count in California was 1,250,000 per site. In 2009 there was an average of 1250 at each site. In There are several factors that are thought to have affected the numbers.

Lack of Food Monarch butterflies’ life cycle includes a caterpillar stage. The caterpillar must feed on milkweed plants or die. There are many varieties of milkweed, some are known as butterfly bushes, but the vast majority are wild plants. Since Roundup-Ready crops were introduced to N. America in 1997, spraying with the herbicide has drastically reduced the milkweed plants. Before GM field crops, milkweed was a nuisance plant growing among the corn or soybeans. It thrives best on the wild prairie grasslands which are increasingly coming under cultivation. Adults need a steady supply of flowering plants to provide nectar.

Habitat Loss Illegal logging of the forests in Mexico has led to fewer and fewer wintering options for the colorful insect. Mexico has set aside the Monarch Butterfly Biosphere Reserve for their winter sleep, but is struggling with illegal logging and grazing in the reserve. In California, loss of habitat threatens the  trees that the insects depend on.

Human Disturbance Humans can carelessly disturb the wintering of the monarchs leading to excess deaths due to running out of fat reserves. 

Climate Change Butterflies are delicate creatures and can be adversely affected by extreme weather events. A heavy rainstorm when it usually is dry may wipe out half a local population. Strong winds may blow the insects away from their usual range.

There are steps that can be undertaken to try to save these unique migratory insects from an early extinction. Some groups are raising milkweed plants, saving the seed and distributing it in the mid west. Others are trying to save more habitat and roost trees while educating the public to the amazing and very delicate natural phenomenon before them. 

The US Forest Service has a very informative site to learn more about one of Gaia’s little jewels.