The Mighty Monarch!
Posted on August 14, 2020
The Monarch butterfly, that familiar black and orange insect seen fluttering about in the summer, is well known for its remarkable yearly migration. Each year, when the days begin to get shorter and cooler, millions of the butterflies instinctively leave their breeding grounds in the Northern U.S. and Canada and head south to the Oyamel fir forests in central Mexico—an epic journey of up to 3,000 miles. Then when the days start getting longer again in the spring, they do the entire journey in reverse.
Given that a monarch’s lifespan is only about 4-5 weeks, these migratory trips occur over several generations each way, with a few generations in between that spend their entire lives in one place or the other. In the spring for example, a generation will emerge in Mexico and immediately begin their journey north. Along the way, they will lay eggs. The new generation instinctively continues north, laying their eggs along the way; and so on. It can take 4 or 5 generations to reach the northernmost part of their breeding grounds in Canada.
Female Monarchs lay their eggs exclusively on milkweed plants. When the eggs hatch, the resulting caterpillars' number one priority is to feed. They only eat milkweed, which is why the eggs are laid there. After about two week of eating and growing, they spin a protective case around themselves and enter the pupa, or “chrysalis” stage. A week or two later, they emerge as fully formed butterflies.
As you’ve probably gathered, milkweed is very important to the Monarch’s life cycle. Not only is it their only food source in the caterpillar stage, it also helps them in their adult butterfly stage as a defense mechanism. Milkweed is toxic to all other animals but Monarchs; and in fact, they are able to store the toxins in their bodies throughout their lives. This makes them poisonous to predators like birds. Their bright colors and distinctive patterns serve as a warning to these potential predators: “Stay away, I taste bad and will make you sick.“
Unfortunately, there has been a significant reduction in milkweed plants in the Monarch’s habitat due to increased use of herbicides in agriculture and mowing along roadsides and ditches. This is obviously a huge problem for Monarchs, and is a major contributor to the alarming estimated 80% decline in their population over the past 40 years. Another threat they face is climate change. They are very sensitive to temperature and weather changes, which can affect biological systems and mess up their migration timing.
Want to help out our Monarchs? The best thing you can do is plant some milkweed! Just make sure it’s the kind that is native to your region.