The Swamp Stomp
Volume 19, Issue 2
Since 1997, the Xerces Society for Invertebrate Conservation has organized a count of the migrating western m butterfly. This was initiated when a large decline in the population of the monarch was noticed in that year. Since then, the count has been taken annually at Thanksgiving, along their migratory path to Mexico and California.
“In 1996, migrating monarchs covered 45 acres of forest in central Mexico, each acre holding an estimated 25 million butterflies. In December 2013, the butterflies covered a mere 1.5 acres. In California, the monarch population has dropped by an estimated 80 percent over the past 15 years.”3. Scientists fear the species will become extinct within the next 20 years, according to a study published in 2017 in the journal, Biological Conservation. Chip Taylor, founder and director of Monarch Watch, states, “Monarchs are symbolic of what’s happening on a larger scale, you eliminate monarchs, and you eliminate everything else that shares that habitat.”3.
The decline in Migrating Monarch Butterflies has become more and more alarming. Although the Western Monarchs have migrated through the western US for centuries, a graph of the last 30 years shows an almost exponential rate of decline. The decline has numerous causes: climate change, deforestation/habitat loss, and the agricultural use of pesticides and herbicides.3. These “problems” can all be traced back to the rapid decline of the milkweed plant in their habitat.
Monarch butterflies are fully dependent on milkweed throughout the growing season of the perennial, so a decline in milkweed populations would greatly influence western monarch butterfly populations. If you’re like most, you might not realize that the monarch butterfly cannot survive without the ample presence of milkweed. This perennial plant is the only plant on which the monarch will lay its eggs. Once the larvae hatch, the caterpillar eats the plant. The two organisms exist in a symbiotic relationship because as the milkweed feeds the caterpillar, the butterfly helps pollinate the milkweed.
For many years, since milkweed is not a cash crop, farmers have removed milkweed fields to grow more corn and soy beans. Whole prairies of milkweed have been mowed to the detriment of the milkweed plant. “A large swath of land that is traveled by monarchs runs through the American corn belt, where most of the crops grown are now genetically engineered and heavily doused with herbicides for weed control.”
Each year, there are four generations of monarch butterflies that can exist. The migrating monarchs begin by laying eggs on their journey north after hibernation. These eggs are the beginning of the next generation for the coming year. The eggs from the first generation of butterflies become the second generation, and so on. The first three generations’ life cycles are consistent. Each generation of a butterfly’s life cycle takes about 2 months to complete.
The fourth generation’s life cycle however, is longer (from 6-8months) and much different. These are the migrating monarch butterflies – eggs laid by the third generation in the September/October time frame. When these butterflies hatch, they know their southern path to the warmer climate. The monarch is the only non-bird species that migrates over 2,500 miles to a warmer climate.
The monarch butterflies will spend their winter hibernation in Mexico if they live east of the Rocky Mountains. If they live west of the Rocky Mountains they hibernate in Southern California. Interestingly, monarch butterflies use the very same trees each year when they migrate. “Most people don’t understand that the monarch, like so many other insects, have a symbiotic relationship with the plant world,” Flanagan said. “They’re connected to the plant world and so when we’re not seeing them, we have to question what’s going on in the plant world.”2.
Those that want to help the monarch butterfly can do so by creating monarch habitats, planting native gardens, and by helping scientists track the species. For additional ways you can help, please see the USFWS “Save the Monarch Butterfly” website.
butterfly population in California plummeted 86 percent in 1 year.” ABC News 7, Chicago, IL, January 12,
Audra, “Agency Sees Decline in Migrating Monarch Butterflies,” NBC News, San
Diego, CA, January 11, 2019, https://www.nbcsandiego.com/news/local/Western-Monarch-Butterfly-Population-Decline-Encinitas-Butterfly-Farm-504212961.html
“Lowly milkweed may be key to monarch recovery,” The Arizona Republic, April
27, 2014. https://www.usatoday.com/story/weather/2014/04/27/monarch-butterflies-milkweed/8226397/