This week for Flora and Fauna Friday our guest needs no introduction, the Monarch (Danius plexippus).
The Monarch is a large butterfly in the Brushfoot family. They’re rich in a burnt-orange above that’s divided by veins of black within black borders. The fringes of their wings are spattered with numerous white polka-dots that spread downward across their downy black body.
Monarchs are interesting in that they feed on Milkweed, a plant that produces a white sap full of toxins. The chemicals in this sap induce cardiac arrest in vertebrates, so herbivores avoid it. Monarchs use this poison to their own advantage. By eating exclusively Milkweed the caterpillars can incorporate these toxins into their bodies, making them as deadly as the plant. However, being poisonous is only useful if the thing that wants to eat you knows about it before it eats you. Otherwise you both end up dead.
Monarchs advertise their toxicity through coloration. Orange and black are the universal colors of danger in the animal kingdom. This patterning is called aposematic coloration and it’s a double-edged sword. Being colorful makes you super obvious to predators, which is a blessing and a curse. On one hand, it decreases your chance of being attacked if the would be attacker can read your pattern. Yet on the other hand, it places you in greater danger from an unobservant, unknowing, or uncaring predator. On top of this, some animals only pretend to be toxic to bluff predators. The Viceroy butterfly is a good example of this and it does an admirable job mimicking our Monarch. Mimics further complicate this predator-poison-prey relationship, turning it into a guessing game for all involved.
The Monarch is a rock star of entomology. It’s one of the few bugs that‘s famous rather than infamous. Regrettably, they’re famous due to their perilous position. Monarchs are a migratory butterfly. Butterflies don’t migrate in the same way birds do, circuiting the continent annually throughout their lives. Instead, butterflies make multi-generation migrations. In late summer, Monarchs begin flying south. They channel down our coastline, flowing from beach to beach in undulating orange waves like an autumn breeze over the ocean. Most make their way to Mexico, although many of those local to the Lowcountry snowbird in Florida instead. Here the butterflies overwinter. When spring sets in the tattered and battered critters fly north in rolling winds. A pilgrimage to lay their eggs over the Milkweed of the Southern US before returning to the Earth. Their children and grand-children continue to leapfrog up the states until winter begins again. The next butterflies to land south of the border are often the great-great-grandchildren of those who made the journey the year before. The Monarch is in danger because of this drawn out migration and its specialized larval diet. Expanding residential development in the Midwest and the over-reliance on pesticides in agriculture are destroying their Milkweed nurseries. The over-development of barrier islands is degrading the corridors of wildflowers they rely on as they migrate through on their way south. On top of that, uncontrollable logging on the mountains of Central America is erasing their wintering grounds. Across the board, Monarchs are getting hammered. They’re not in danger of going extinct but the possibility of this annual journey perishing, reducing the species to but a few sedentary populations, is very much real.
