Monarchs & Milkweeds

The gorgeous American Monarch butterflies (Danaus plexippus), with their orange wings, black veining and a distinctive black and white checkered pattern around the margins, are instantly recognizable by gardeners and non-gardeners alike. As a defense against predators, Monarch butterflies contain unpalatable chemicals that can actually cause some birds to vomit! And their bold wing pattern is a well-known warning to hungry birds that they should not trifle with those Monarchs.

By current estimates, the overall number of American Monarchs has fallen by 90% in the last decade. The decline of Monarchs is directly linked to the loss of milkweed plants in the wild. Milkweeds (all members of the genus Asclepias) are the host plants for Monarchs, meaning Milkweeds are the ONLY PLANT that Monarch larvae are able to eat, and the only plant where adult Monarch butterflies will lay their eggs.

What's contributing to the loss of milkweed plants across the country? Today, before beginning their spring planting, conventional farmers (those who do not use organic practices) will spray their fields with chemicals to eradicate weeds. Unfortunately, his practice also kills all the wildflowers, including the Milkweeds, that surround those fields. Also, as cities, towns, and neighborhoods expand, wild open meadows where native milkweed is typically found are disappearing. 

The good news is that our gardens can make a difference!

The amazing life cycle of the American Monarchs. If we are to reverse the appalling decline of these butterflies, it is helpful to understand more about of the remarkable life story of the American Monarch.

Eastern Monarchs

In the summertime, Eastern Monarchs can be found all the way from Mexico to southern Canada, and from the Rocky Mountains to the Eastern seaboard. All across this huge land area, four or sometimes five generations of Monarchs are born in a single season!

Starting in September and October, all Eastern Monarchs, (with the exception of a few that use the Atlantic seaboard) undertake a single prodigious migration to reach their over-wintering destination, the Monarch Butterfly Biosphere Reserve, in Southern Mexico.

During this migration, these tiny creatures fly the most astonishing distances. Those that begin their journey in the Canadian Maritime provinces will travel nearly five thousand miles to reach their winter destination in Central Mexico. Butterflies begin their fall migration in September or October, and finally reach their overwintering sanctuary in November.

The following March, those same butterflies set out on their northbound trip. However, no individual butterfly flies all the way north: At successive stops along the way, the female monarchs lay eggs on milkweed plants, and the resulting caterpillars initiate the new generation of butterflies that continue the journey northwards. It is estimated that in the course of the entire summer, eventually four or five generations will be raised.

In early fall, the final generation of females store their food supply in preparation for their long flight back to Mexico, instead of producing more eggs. These butterflies are also programmed to fly south or south-west depending on their starting points, to reach this single destination.

Check out this wonderful interactive map to see the flight paths taken by the butterflies during their trip south in the fall, as well as how the successive generations that are raised on the way north in the course of a single summer.

Western Monarchs

Like their eastern counterparts, the Western Monarch butterflies also have a migratory life cycle. Their summer territory is to the west of the Rocky Mountains, where typically, they will hatch three generations at successive points along those fly-ways.

Every fall, the third generation of these butterflies is programmed head south-west to reach one of several over-wintering destinations along the west coast of California and western Mexico.

Non-Migratory Monarchs

Unlike the Eastern and Western populations, American Monarch butterflies that are found in Florida and along the Gulf Coast do not migrate. This minor population remains in this warm climate on a year-round basis.