The monarch butterfly (Danaus plexippus) is probably the most easily recognizable insect in North America. Don’t let this butterfly’s beautiful and delicate demeanor fool you, however. These little guys make an incredible 1,200 to 2,800 mile journey from their overwintering habitat in Mexico, all the way to the northern United States and Canada. Unfortunately, monarch butterfly populations have been on the decline for the past several decades, and scientists have identified several potential causes for their decreasing numbers. While some of the threats to monarchs have been identified, further research is needed in order to determine the best possible plan to protect this iconic species.
The monarch butterfly’s migration is a multigenerational cycle in which adults move north toward Texas to reproduce, and the offspring of those butterflies move farther north in order to continue the journey. During this migration, the monarch relies on the milkweed plant as its main habitat and food source in order to ensure its survival. Habitat loss of milkweed, however, is one of multiple threats that the monarch is currently facing.
“Monarch feeding on swamp milkweed Sand Lake NWR” by Tom Koerner/USFWS is licensed under CC BY 2.0
According to a recent article written by Alcock, Brower, and Williams, the use of herbicides on herbicide resistant plants in the United States has been related to loss of milkweeds. These scientists postulated that because the monarch uses milkweed for breeding, the decline in habitat is leading to population collapse of this species (Alcock, Brower, and Williams, 2016).
Efforts to protect the monarch butterfly should include restoration of the declining milkweed populations. Alcock, Brower, and Williams studied the effects of mowing milkweeds in areas of Virginia that monarchs visit during their migration.
According to their research, mowing milkweeds during the growing season can lead to regeneration of the milkweed plants. Milkweed mowing may thus provide more resources for monarchs later in the season when they lay their eggs on these plants (Alcock, Brower, and Williams, 2016). Because both humans and monarchs rely on the monarch’s habitat, it is critical to find ways to protect has much of the habitat as possible for the butterflies.
The results show that mowing of overgrown milkweed fields extended the breeding period for monarchs by three weeks in mowed fields compared to unmowed fields (Alcock, Brower, and Williams, 2016). Earlier findings from a study completed in New York show similar outcomes where mowing extended the breeding period by approximately two weeks (Fischer et al, 2015).
While this evidence may seem promising for the future of the monarch in North America, more research is needed to determine the best milkweed mowing routines at various latitudes to provide optimal conservation of the milkweed. Because timing is so crucial for milkweed mowing and regeneration, it is essential that the proper timing for mowing be determined at varying locations along the monarch’s migration route.
According to Alcock, Brower, and Williams, “If properly timed mowing were instituted on a broad scale, the current widespread loss of milkweeds suitable for monarch caterpillars caused by the increasing use of herbicides on household landscapes, commercial agricultural crops, roadsides, and power and gas line right-of-ways might be ameliorated to some degree.” Monarchs are losing their habitat as a result of human disruption, so it is imperative that we do what we can to restore this habitat before the situation escalates.
There are critics of the hypothesis that monarch populations have declined as a result of limited milkweed (Inamine et al, 2016). According to Inamine et al, it is unlikely that loss of milkweed is causing the monarch’s decreasing numbers. According to this study, threats during the monarch’s fall migration when monarchs are not using milkweed are to blame for the population’s decline (Inamine et al, 2016). However, considering milkweed is the only habitat for monarchs, protecting their environment is a step in the right direction to protecting the species overall.
Although there has been tremendous research conducted on the monarch and the factors that influence their migration, further investigation is required to truly understand the complexity of this marvelous species. While conservation of the milkweed may not be the only answer to protecting the monarch butterfly from total population decline, it is certainly a good place to start.
Alock, J., Brower, LP., Williams Jr., EH. 2016. “Monarch butterflies using regenerating milkweeds for reproduction in mowed hayfields in northern Virginia. “ Journal of the Lepidopterists’ Society. 70(3): 77-181. Web. 4 Sept. 2016.
Fischer, SJ. Williams, EH., Brower, LP., Palmiotto, PA. 2015. “Enhancing monarch butterfly reproduction by mowing fields of common milkweek. The American Midland Naturalist Journal. 173: 229-240. Web. 4 Sept. 2016.
Inamine, H. Ellner, SP., Springer, JP., Agrawal, AA. 2016. “Linking the continental migratory cycle of the monarch butterfly to understand its populatin decline” Oikos. 125: 1081-1091. Web. 4 Sept. 2016.