I am willing to bet that most of you River Reporter readers have seen monarch butterflies flitting about your backyard. Monarchs migrate each fall to the mountain forests of Mexico to overwinter; then they return north and east to mate and start a new generation. They go through four stages during one lifecycle, and it takes four generations of monarchs within a year to complete their mating and migrating patterns. Monarchs lay their eggs on milkweed plants, with hatching taking place four days later. The caterpillars (larvae) eat milkweed leaves for about two weeks before forming a chrysalis to begin metamorphosis into an adult butterfly. The previous generation of egg-laying adults die as the new generation enjoys the two to six weeks of life as a butterfly. This process continues until the last generation is complete, with those adults returning to Mexico in the fall.
Because their lifecycle is so complex, Monarchs are subject to a variety of environmental factors that impact them as a species. First of all, monarch butterflies only lay their eggs on milkweed plants; when the eggs hatch, the little caterpillars can only feed on milkweed leaves, making them completely dependent on milkweed for their survival as a species. Nearly 165 million acres of milkweed have been lost over the years due to development and the use of herbicide. As a result, the monarch’s primary food supply and support systems have been significantly compromised.
Annual surveys determined that Monarch populations deceased by more than 80% over the last 20 years. For example, it was estimated that one billion monarchs thrived in the mid-1990s—a number that declined to 93 million by 2008. In fact, the species decline has been so dramatic that in 2104, the U.S. Fish and Wildlife Service was petitioned to protect Monarchs under the “Endangered Species Act.” A decision was expected in June of this year, but was not settled at the time of this writing. More recent population estimates conducted in 2018 found that the area used by monarchs to overwinter in Mexico decreased from 7.19 acres 6.12 acres.
There is some good news. The spring 2109 estimate for monarchs’ wintering in Mexico’s forests, increased from 6.12 to 14.94 acres—a 144% improvement.
Nevertheless, and in spite of that upward spike, it is important to remain vigilant. A one-year increase in a population that has been in serious decline does not mean the species is on a sustained rebound, so it is important for researchers to continue monitoring. It is also important for the general public to be aware of the monarchs’ status and participate in conservation efforts to help restore these wonderful, beautiful butterflies. It appears that the loss of thousands of acres of milkweed habitat, along with the use of a variety of pesticides and herbicides, are the main causes of the monarch’s decline. If those trends can be reversed, it is possible that monarch populations will continue to increase. Let’s all do our part.