Perhaps no insect commands more interest than Danaus Plexippus—the well-known Monarch butterfly. Its flashy physical appearance and distinctive migratory behavior locates this species in a special category. Our readers will bear with us for many past posts on Monarchs, the only butterfly to complete an annual two-way migration.
Before discussing the migratory behavior of Danaus Plexippus, consider some developmental details of this unique animal. Our view is this migratory animal strengthens belief in an Almighty God who sustains the existence of all things. The monarch butterfly epitomizes the wondrous event sequence of four-stage metamorphosis. Adult female Monarchs, after mating with male monarchs, lay individual eggs on milkweed plants. A few days later, they hatch into tiny caterpillars, the larval stage, and begin to feed on milkweed leaves. After more than a thousandfold weight gain in one or two weeks, they suspend themselves upside down for a short time, shed their skin, and transition after 8-12 days into a beautiful jade-colored pupa called a chrysalis. The adult monarch which bursts forth from the chrysalis is a marvel of beauty. But the aesthetic beauty and four-stage metamorphosis of this insect is only part of its story.
Our current post is inspired by an observation we made from our Northwest Illinois front porch during the last week of September. Our residence faces almost directly east. We were privileged to observe a local manifestation of the famous migration of monarch butterflies. We noticed many monarch butterflies all flying above our front lawn from left to right. More precisely, we identified their compass direction of travel: northeast to southwest! I had not observed this directional monarch travel for a number of years. The last time was likely 2006. An encouraging spike in monarch population occurred in 2018—144% greater than the previous year. After many years of alarming declines, the increase is encouraging.
A few days later we traveled to the east coast on Interstate 80—Illinois, Indiana, Ohio, and Pennsylvania. Again we observed every monarch navigating directionally across the Interstate from left to right. I estimated the number of monarch sightings as approximately 20 to 24 per hour. Every monarch was impelled to fly in a specific direction.
The last generation (probably the fourth) in late summer does not reproduce immediately. They return to Mexico after a long and hazardous flight to a small mountain forest. Their journey is followed by a long period of quiescence for several months with millions of other clustered monarchs. This special generation then begins a return journey a few hundred miles to the north. After reproduction, their offspring continue on, producing the second of four broods. Each of the first three broods lives only a few weeks. The fourth brood, from the northern and eastern states and southern Canada, undertakes a long, hazardous return journey at the end of summer to the mountainous Mexican forest. Diminishing day length and cooling temperatures trigger the fourth generation’s divergent behavior. Those travelers have never been to Mexico before!
Monarch migration is unusual because of its two-way, cyclical journey. In contrast, many individual migrating birds annually travel back and forth between their seasonal habitats. The difference between this bird migration and the unique monarch migration is that no individual monarch completes one cycle. In this way monarch migration is even more remarkable than bird migration. Monarchs must blend internal physiological and external cues such as earth’s magnetism, polarized light, and other geographical cues to implement their annual migration. Scientists have calculated that the pinpoint location of their Mexican overwintering forest site is only 0.015% of the area they occupy during their summer sojourn in the Eastern US and Canada.
Some bioscientists call the Danaus Plexippus migration an “evolutionary development.” We must determine the meaning of “evolutionary” in this context. The remarkable migration is necessary because the monarch is unable to survive in the cold, wintry, northern areas of its range. There are several world regions where monarch butterflies are non-migratory—namely southern Florida and smaller populations in Central and South America, Hawaii, South Pacific Islands, Australia, and a few spots in Western Europe. In all cases, we credit monarchs’ adaptability, also a gift of the Creator bestowed on living all things.
Epigenetic adaptation occurs “above or on top of” genetics—the basic information supplied by DNA to all living creatures. Not only does the monarch have a heritage of DNA, but it also has a heritage of epigenetic adaptation. Great quantities of information related to monarch behavior and all other living creatures are becoming accessible as new scientific discoveries uncover the genius of Our Creator.