programs Natural Resources

Monarch Butterfly

(Danaus plexippus)


No insect under review by the U.S. Fish and Wildlife Service (FWS) has received more attention at the highest levels of government than the monarch butterfly. In February 2014, Mexican President Enrique Peña Nieto hosted U.S. President Barack Obama and Canadian Prime Minister Stephen Harper as they committed to helping restore the species while they met to discuss the North American Free Trade Agreement. The bright orange and black butterfly with an annual migration stretching from the central mountains of Mexico to the plains of Canada had come to symbolize the treaty.

The year before the leaders’ meeting in Mexico, the monarch’s population hit an all-time low. The numbers of wintering butterflies, which vary widely, were only at 3 percent of the highest population level 18 years earlier. By August 2014, biologists and conservation groups had filed a petition with the FWS to list the monarch under the Endangered Species Act. By the end of the year, the federal agency announced it would conduct a full review of the species. In 2016, newly elected Canadian Prime Minister Justin Trudeau hosted Presidents Obama and Peña Nieto in Canada. The “three amigos,” as the press called them, again spoke of the monarch and the need to protect it for future generations.

The speeches generated plenty of press attention, but the actual work was not easy. The petition cited the proliferation of herbicide-tolerant crops of soybeans, corn and cotton as a threat to the monarch. These herbicides allowed farmers to eliminate almost all weeds from their land including milkweed, the monarch caterpillar’s sole food source. Also cited were diseases spread by non-native milkweed, sales of captive-bred monarchs disrupting wild migrations and threats of climate change. The FWS is considering these and other factors in its species assessment, which it plans to complete in December 2020.

While the monarch’s overall habitat needs are known – thanks to a massive citizen-science movement in the Midwest and Southern Canada – there is still a significant knowledge gap. Among the unanswered questions are: What happens to the monarchs as they pass through Texas twice each year? What helps the species in the Lone Star State? What harms it?

Research Description

These were the broad areas of inquiry the Texas Comptroller of Public Accounts (CPA) undertook when it contracted with four universities in 2016. The specific studies ranged from vehicle impacts, which kill an estimated 2-4 percent of monarchs migrating across Texas each cycle, to fire ant bites, which were determined not to be a major problem for monarchs. The researchers considered habitat characteristics to determine what the monarchs needed when and where. The results showed that they need more native milkweed and flowering plants everywhere, especially in the spring. Researchers compared different land management practices of prescribed burning, mowing and grazing on habitat to see how they affected the number of milkweed stems and monarch eggs laid. The analysis showed that the timing of the treatments matters and can have a short-term positive impact. Finally, the researchers modeled the distribution of the monarchs and looked at risk factors, which showed that weather is an important variable.

The research provided insight into what is happening in Texas and opened the door for more fact-based discussions about what can be done to assist the species.

Deliverables Provided at Contract End, 2018

  • Reports on:
    • distribution
    • migration patterns
    • studies of the life history of monarchs while in Texas
    • literature reviews
    • best land management practices for milkweed production, along with the impacts of drought and fire ants
    • distribution of different types, density and diversity of milkweed across Texas

Why This Research Matters

Monarch butterflies are a charismatic species that depends on an ecosystem stretching from the Central Mexico to Canada. As such, their fate will depend on the actions of a very broad group of people, along with the weather patterns and trends of an entire continent. Because Texas acts as a funnel between the monarchs’ summering grounds in Canada and the northern United States and their wintering grounds in Mexico, what happens here likely will have a disproportionate impact on the species’ future. This research is important because it helps inform discussions of what should and can happen in Texas to preserve the monarch’s migration.