Sunday, August 10, 2008

Flight of the Monarchs

Monarchs are known for their extraordinary annual migration. In North America they make massive southward migrations starting in August until the first frost. A northward migration takes place in the spring. Female monarchs lay eggs for the next generation during these migrations.

By the end of October, the monarch population of the Rocky Mountains migrates to the sanctuaries of the Mariposa Monarca Biosphere Reserve in Mexico. The western monarchs overwinter in various sites in central coastal and southern California. (Most notably in Pacific Grove and Santa Cruz.)

What is even more remarkable is that the ones that return to the places where Monarchs hibernate have never been there before. They are the great-great-great-grandchildren of those that performed the journey from southeast Canada and the United States to central Mexico.

The monarch (Danaus plexippus) is a milkweed butterfly and is perhaps the best known of all butterflies. Since the 19th century, it is also found in New Zealand, and has been known in Australia since 1871. Its wings feature an easily recognizable orange and black pattern, with a wingspan of about 4 inches. Female monarchs have darker veins on their wings, and the males have a spot in the center of each hind wing from which pheromones are released. Males are also slightly larger.

Monarch butterflies are one of the few insects capable of making transatlantic crossings. They are becoming more common in Bermuda due to increased usage of milkweed as an ornamental plant in flower gardens and remain year round due to the island's mild climate.

Monarch larvae appear to feed exclusively on milkweeds in the genus Asclepias. Milkweeds are perennial plants, growing each spring from rootstock and seeds rather than seeds alone. There are approximately 110 species in North America known for their milky sap or latex contained in the leaves. Most species of milkweed are poisonous to vertebrate herbivores if due to the alkaloids contained in the leaves and stems.

When Monarch larvae ingest milkweed, they also ingest the plants' toxins, called cardiac glycosides. This causes the larvae and adults to be toxic to many potential predators. Vertebrate predators may avoid Monarchs because they learn that the larvae and adults taste bad and/or make them vomit. There is considerable variation in the amount of toxins in different species of plants. Some northern species of milkweed contain almost no toxins while others seem to contain so much of the toxins that they are lethal even to monarch caterpillars.

Habitat destruction throughout North America is resulting in the loss of milkweed and the reduction of overwintering habitat. One way you can help is by planting a butterfly garden.
Planting a butterfly garden will enable you to watch not only monarchs but also many other butterfly species right in your backyard.

The Butterfly Website has a nice page devoted to butterfly gardens, and organic gardening. Needless to say, the use of pesticides on your plants is not conducive to a healthy butterfly population, so read up on organic gardening techniques. Enjoy the beauty of flowers and create a healthy habitat for insect and bird species in your own backyard!

Until next time, become the change you imagine.

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