Monarch – Migration of Multiple Lifetimes

Monarch Butterfly I captured in my neighborhood

This is a Monarch Butterfly (Danaus plexippus).  These are very interesting little critters for many reasons.  The first reason is because they are very beautiful, both larvae and adult. The larvae (as pictured at the end of the post) is brightly colored and very pleasing to the eyes, but the adult is even more beautiful and hardly goes unnoticed.  The way Monarchs are allowed to have these bright colors and survive predation is due to the fact that they are toxic to other organisms.  Adult Monarchs lay there eggs on species of Milkweed (Asclepias sp.), which contain cardenolide aglycones.  These cardenolide aglycones are steroids which can cause their predators hearts to stop.  The monarch larvae store these compounds in their bodies, making them toxic when ingested (this is also maintained in the adult).  Predators now know to stay away form both the larvae and the adult Monarchs.  This is so successful that other butterfly species have evolved to mimic the Monarch to keep predation at bay (examples are the Queen and the Viceroy Butterflies).  Monarchs are also important natural pollinators in North America.  The adult Monarchs are constantly feeding on nectar of different plants and migrating, which is spreading pollen around for these plants.  They are an important natural pollinator that have evolved to specialize on certain plants (like milkweed, asters, Baccharis sp., just to name a few) and the pollination of these plants is altered as the Monarch population declines.

Monarchs are also very interesting because they have one of the most magnificent migration patterns on the planet.  They travel from an area in the Mexican Highlands (around 2 miles above sea level) where they roost in the winter in Oyamel Fir Forests, and they go north approximately 3,000 miles into Canada.  They are though to do this because Milkweed does not grow in their southern grounds, but it is too cold to survive in the northern part of their range where the Milkweed does grow.  The interesting part about this trip is that it is multigenerational, which means that the individual Monarch that takes off from Mexico does not return back.  Instead, it takes 3-4 generations for the Monarchs to get to the northern most part of their range.  Although, once the lineage turns south, One individual adult Monarch makes the long trip all the way south back to Mexico (there are some other southern areas such as the Rocky Mounts of Southern California and some Caribbean Islands, but Mexico is by far the largest).  The Adults we are seeing in the late fall/early winter here in South Carolina are these tough butterflies making their way south.  These butterflies travel by day, and congregate together at night in trees or brush to stay warm.  It is thought that they use the magnetic pull of the Earth to know direction.

These are very cool organisms and it is lucky we get to see them.  Recent studies have shown that their numbers are declining at an alarming rate.  They are dependent upon Milkweed for their larvae to survive.  Even though Milkweed grows naturally virtually everywhere in the US, many people see it as a “weedy” species and try to get rid of it.  Because of development, clear cutting farmland, and herbicide use, the amount of Milkweed has declined drastically.  Because of the Milkweed decline, the numbers of Monarchs has dropped as well.  One thing you can do for these organisms is next time you go buy plants for your flower garden, throw in some Milkweed.  It is very pretty, easy to grow, and will attract these awesome butterflies to your backyard.  Its a small price to pay to help out with the conservation of these beautiful creatures.

Monarch Larvae

For more info on these guys click here


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