Saving the monarch butterfly

Saving the Monarch Butterfly

Lauren Bennett | October 13, 2018

The migration of Monarch Butterflies is so spectacular that it attracts international tourism to regions of the U.S., Canada and Mexico every year. Climate change adversely affects integral parts of the Monarch’s life cycle. Rising temperatures in the region change the climate cues for Monarchs that threaten to diminish the spectacle of their migration forever and endanger the species. Climate change also reduces the Monarch’s main food source and threatens its winter habitat. Deforestation and harmful chemicals further compound climate induced stress on the Monarch population.

While the Monarch is not yet doomed, this charismatic and universally admired species will be in great danger unless preventative steps are taken that mitigate climate change, preserve Milkweed, and protect Oyamel Fir forests.

Why is Migration Important?

Migration is an integral part of Monarch Butterfly survival. As the weather begins to cool in parts of Canada and the United States, Monarchs begin their long journey to Mexico, traveling up to 3,000 miles. This migration takes approximately five months, spanning from the end of October until March. The annual change in atmospheric temperature provokes Monarchs to begin their long southward migration, allowing them to avoid harsh Canadian winters. It is in Mexico that they spend their winters conserving energy in its Oyamel Fir Tree forests. According to Bittel, these trees “create a microclimate that protects the insects.” Bittel goes on to say that “The tree canopy and ecosystem provide a blanket effect for the Monarchs, so the temperatures do not go too high or too low.”

In the spring, Monarchs begin to lay their eggs on their main source of food, Milkweed, ensuring that when their larvae hatch, they have a readily available food source.

In the summertime, Monarchs make their long journey back to Canada and the U.S. Several generations will have passed before they make it back. In fact, in the fall, a special generation of Monarch Butterflies, sometimes referred to as a “super generation” will emerge that can survive up to eight months, much longer than other generations that only live five to seven weeks.

Although Monarchs have adapted their migration patterns to dynamic conditions in the past, they are likely unprepared for the rapid climate change seen today that will alter their ability to rely on the natural rhythm of their weather dependent cycles.

Climate Change Impacts

There are many ways in which climate change impacts Monarch Butterfly migration patterns and, in turn, their survival. Not only does climate change influence climate cues that Monarchs use to navigate and begin their migration, but it also impacts their food sources and overwintering habitats.

Migration

Monarch Butterflies greatly rely on the cue of colder weather to not only prompt their migration to Mexico, but also their return to Canada and the U.S. According to Narayanan, if cold temperatures do not cue their return back to the U.S. and Canada, then Monarchs will simply continue to migrate further south, moving away from their natural habitat.

Monarch Butterflies spend winters in Mexico, allowing them to survive the harsh environments of Canada and the United States. Although Mexico has long been the Butterflies’ safe haven in the winter, climate related events threaten the population of Monarchs in their winter habitat.  An intense storm in 2002, for example, wiped out an astounding 80% of the migrating population of Monarch Butterflies in their winter habitat. This is a particular concern because climate change has been linked to the frequency of intense hurricanes.

According to the World Wildlife Organization, climate change also disrupts Monarchs’ migration patterns by inducing wetter and colder winters that lead to a more inhospitable environment for Monarchs. The effect is an increasingly more dangerous migration route for the butterflies.

Milkweed

Climate change not only affects Monarch migration, but it also influences the availability Milkweed, which is not only their main food source, but also a refuge for eggs. Milkweed produces a poisonous chemical called cardenolide. Harmful to other insects and animals, Monarchs have built up a tolerance for certain amounts of the poison. Larvae are safe when they hatch on Milkweed because predators cannot eat them without the risk of getting poisoned. Because their Milkweed intake makes Monarchs themselves poisonous, their diet also deters predators of adult butterflies. In fact, their spectacular colors warn potential predators of the poisonous content.

Climate change threatens the Monarch’s food supply. When Milkweed senses warming temperatures, it increases the amount of cardenolide as a defense mechanism from the plant’s predators. This can be detrimental to Monarchs. Although they have a tolerance to the poison, they are not invincible to certain concentrations.   The increased cardenolide levels in Milkweed present in warmer temperature poses a threat to both adult Monarchs and their larvae. It may become possible for the butterflies’ primary food source to become intolerably poisonous to them, a potentially disastrous outcome for the species.

Herbicide use in the agricultural industry further compounds the Monarch’s Milkweed problems. Not only is the butterfly’s food source becoming intolerably poisonous, the safe sources of Milkweed are running low. According to Hance (2015), when the soy and corn industries moved into other agricultural fields, it killed 58% of U.S. Milkweed population from 1999-2010. Hance continues to say that this takeover directly affected Monarch populations by a devastating 81%.

Habitat loss 

Oyamel Fir Trees, as discussed earlier, create a microclimate for Monarch Butterflies to overwinter in Mexico. Due to climate change and deforestation these fir trees are also disappearing, leaving less land for Monarchs to be protected from the elements. The lack of suitable environments for these butterflies to occupy during winters in Mexico further stresses the Monarch’s survival.

Mitigation Strategies

While Monarchs are already on the Species of Special Concern List, many scientists and industry professionals have requested petitions to upgrade their protection by adding the Monarch Butterfly to the Endangered Species List.

Given their declining population, steps must be taken to ensure that the population of Monarch Butterflies recovers. Several mitigation strategies that can aid conservation of this charismatic species:

Habitat Conservation

With Oyamel Fir Trees disappearing due to legal and illegal logging practices, it is imperative that more responsible logging practices are implemented and that existing regulations are enforced. The conservation of Oyamel Fir Trees should become a focus in the conservation of Monarch Butterflies.

This can be accomplished by banning or adjusting the number of trees which can be logged each year, taking into account the space that Monarchs need to survive the winter.

Milkweed

Restoring the Milkweed population would greatly increase Monarch food supply and keep the butterfly safe from predators. Implementing firmer guidelines in the use of herbicides could help accomplish this. Guidelines on herbicides should be used in areas that are near Milkweed and should also include the method in which herbicides are applied to farms and other agricultural areas. For example, if a crop treated with herbicide is close to a field with Milkweed, that crop would not be sprayed with herbicide as spraying increases the risk of the herbicide reaching and killing nearby plants.

This is also an area in which citizen scientists can become involved. It would be helpful to Monarch populations if those that live near any point of their migration route would plant Milkweed on their property. The added benefit would be a front row seat to the Butterfly’s spectacular migration.

Conclusion

Several factors contribute to the decline of Monarch Butterfly populations. Climate change poses severe risks that threaten their food supply and habitat. As long as global warming takes place, the Monarch Butterfly will be threatened. Governments, industries, and citizens can take more immediate steps to mitigate other threats to butterflies. More responsible logging practices, reduced herbicide use, and Milkweed preservation would give the Monarch Butterfly population a chance to recover.

Lauren Bennett is a Graduate Research Fellow at the Climate Institute