The Remarkable Monarch

Meet Danaus plexippus – the Monarch butterfly – in larval stage.

click on image to enlarge

This teensy-tiny fella - about a single centimeter in length - is posing on one of the many, many milkweed plants at our house on the peninsula.

Adult butterflies feed on the nectar of flowers but in its larval stage of life the monarch feeds exclusively on milkweed.  This endows it with a unique defense mechanism.  The monarch is poisonous to predators as a consequence of dining upon milkweed.  Toxic chemicals found in milkweed build-up and remain in the critter even after it metamorphoses into a butterfly giving it a chemical defense system.  Remarkable!

This caterpillar will form a chrysalis from which an adult butterfly will emerge.  The entire process of egg, caterpillar, chrysalis, and butterfly takes about four weeks with multiple generations born over the course of a year.

This insect is even more remarkable when you consider its travels.  Monarchs migrate up to several thousand miles from Mexico to Canada and back.  Beginning in the spring migrating females head north in relays laying their eggs along the way with new generations of butterflies replacing the old.  Each butterfly will migrate once with its great-grandchildren migrating the following year.  The science behind the migration supposes that the monarchs use the earth’s magnetic field to navigate and the position of the sun to signal when to depart for Mexico.

Since the butterfly only lives a few weeks it is the last generation of monarchs born in late summer or early fall that make the migration.  As the temperatures begin to fall and the days grow shorter this generation of butterflies doesn’t mature enough to reproduce allowing them to live up to eight or nine months.  They’ll make the migration south for the winter and return next year to reproduce.

Monarch numbers are in decline as a consequence of pesticide and herbicide use and loss of habitat.  If you’re inclined to lending a hand plant milkweed and nectar producing flowers for this amazing animal.