Monarch Butterflies

The monarch is North America’s best-known butterfly. It’s large and showy, with distinctive markings. Its wings are bright orange with black veins, black borders, and white spots on the borders. But what makes the monarch truly notable is its migratory habit. Every fall, millions of monarch butterflies migrate to the warmer climates of California and Mexico, where they overwinter. For some of these butterflies, that migration is almost 5,000 kilometers long. It’s truly an amazing journey for an insect that weighs, on average, 50 grams.  

Monarch Life Cycle 

Like all butterflies, monarchs (Danaus plexippus) have a four-phase life cycle: egg, larva, pupa, and adult. 

Egg 

Life begins for a monarch when a female butterfly deposits her egg on a milkweed plant. Other species of butterflies may lay several eggs at one time. However, a monarch butterfly deposits her eggs one-by-one. She may lay several hundred eggs throughout her life. The eggs are tiny–about 1mm in diameter. They are usually deposited on the underside of a milkweed leaf to keep it safe. 

Larva 

According to the NatureWatch website, larvae (caterpillars) typically hatch within 3-8 days. The larva starts life by eating its egg casing and then begins to feed on the milkweed plant it hatched on. Larvae don’t move around or do very much other than eat and grow. As they grow, their exoskeletons become too small and the larvae molt or shed their skin. Monarch larvae go through this process four times. And, with each success molt, their striking black, gold, and white stripes become more distinctive.  

The larval stage of life lasts about 10 to 14 days. 

Pupa 

When it’s time to pupate (go through metamorphosis to become a butterfly), larvae will seek a safe spot to form its chrysalis. Many monarch larvae stay on their host milkweed plant and attach their chrysalides to the underside of milkweed leaves or stems. But, some may wander off and choose a different spot to pupate. 

It takes 8-15 days for a monarch butterfly to complete the pupation stage. As explained at the Gardens with Wings website, the process is quite amazing:  

The insect’s body basically is liquefied by digestive fluids and the body is restructured using specialized formative cells. This process is called histogenesis, in which undifferentiated cells are used to build different body tissues.  

Sometimes, metamorphosed butterflies will remain inside their chrysalides for a little while. They’ll rest there until something triggers them to emerge. Those triggers, as explained in a piece at ThoughtCo, may be changes in light or temperature, or chemical or hormonal signals.  

Adult Butterfly 

Many adult monarchs live for only two to six weeks after emerging from their chrysalides. They begin mating very quickly after emerging, so that the population’s life cycle may continue.  

The exception is with monarchs that emerge in late summer. Those are the butterflies that will make the trek to California or Mexico. They need a longer lifespan to survive the journey. These late-season monarchs may live for 6-9 months.  

Monarchs and Milkweed 

According to the Lady Bird Johnson Wildflower Centre, common milkweed (Asclepias syriaca L.) is found throughout the midwest and eastern North America. It is actually a poisonous plant. It’s those poisonous properties that make it valuable to monarchs. As pointed out at the Espace pour la vie website, as monarch larvae consume milkweed, the plant’s toxins accumulate in the insect’s body. That toxicity makes the larvae and the adult butterflies unpalatable and slightly toxic to many predators. 

Brightly coloured appearances often hinder wildlife, as the bright shades make them easy for predators to spot. But, in the case of monarchs, their bright colours serve as a warning to predators that they don’t taste good and may even be poisonous. 

The Migration of Monarchs 

As late summer merges into fall, monarch butterflies start their annual migration south. Butterflies that emerge from their chrysalides at this time don’t fully develop their reproductive organs. This allows them to save their energy for the migration.  

Using a combination of air currents and thermals, some of the butterflies travel about 5,000 kilometers to their winter habitats. As the U. S. Forest Service explains, monarchs from eastern North America travel to the Sierra Madre Mountains in Mexico, while monarchs from the western areas of North America have a shorter journey to California. 

Monarch butterflies spend the months of November through March in their southern habitat before they start migrating back north. Interestingly, monarchs live out their regular springtime life cycles on the journey north, transforming from egg to larva to pupa to butterfly along the way. The generation that arrives in their northern summer homes is several generations removed from those butterflies that began the trek back from the south. 

The Importance of Monarch Butterflies 

Given their numbers and the area they cover monarchs are important pollinators. And pollinators are crucial to continued human health and wellness. 

There are other reasons monarchs are important as well. They’re often used as models in the school systems, to teach children about the life cycle of butterflies and the mysteries of migration. The decline in their population has prompted conservation efforts. It has also helped to discourage the use of chemical fertilizers, pesticides, and herbicides. 

Additionally, the monarch butterfly is considered an “indicator species.” Since the insects are quite sensitive to climate change as well as to harmful chemicals, changes to their population numbers are an important indicator of environmental and ecological health. 

Environmental Status of Monarch Butterflies 

The decline of monarch butterflies is a serious concern. The Centre for Biological Diversity (CBD) explains that between 1994 and 2016, the number of monarch butterflies had declined by a startling 68%. Because of this sharp decline, the CBD petitioned the U. S. government to declare that monarch butterflies are a “threatened” species under the Endangered Species Act. As of late 2019, that petition is still under review. 

In Canada, monarch butterflies have the status of “special concern.” This means that their population is not currently considered threatened or endangered, but that might change. 

Monarch populations are vulnerable mainly due to habitat loss at their overwintering sites. Those forested sites are being stripped of trees and converted into agricultural lands. However, the widespread use of chemical pesticides and herbicides is also a cause for concern. Herbicides affect the growth of milkweed, which is crucial to the survival of monarchs. 

However, 2019 saw a resurgence in monarch numbers–a 144% increase, in fact, as reported by the CBC. Researchers speculate that warm weather in Texas allowed milkweed to flourish in that state, which in turn supported larger numbers of monarchs on their return migration north. Those same researchers are hopeful that the upward trend will continue. We should all hope the same. Not only are monarchs a beautiful part of our ecosystem, but they are crucial to the maintenance of human life as well.