September 23, 2020

Monarchs and Milkweed

Monarch MigrationYou might not get to Mexico this winter, but if you plant some milkweed, you can help a Monarch Butterfly get there.

With their bright orange and black wings, monarchs are one of the most easily recognizable butterflies in the U.S. and Canada.  But where do they come from?  The monarch in your garden is like a long-haul trucker stopping for a meal.  This little creature travels hundreds or thousands of miles in its lifetime.  You can be part of this incredible journey by planting milkweed, the one plant absolutely essential to the monarch’s life-cycle.  See the video at the bottom of this post for more information.

Monarchs are well known for their long-distance migration.  Each fall, they fly thousands of miles on their delicate wings to ancestral roosting sites, where they spend the winter months semi-dormant in large colonies.  Western monarchs migrate to dozens of locations along the California coast, where they cluster in native trees and in the ubiquitous non-native eucalyptus.

East of the Rockies, monarchs make a more dramatic migration.  They fly from southern Canada and the northern United States all the way down to a handful of sites in the mountains of Mexico, where they roost in the millions.  It’s breathtaking to see so many monarchs in the trees that their collective weitht sometimes breaks branches, and to hear the sound of millions of butterfly wings when the monarchs take flight to sip from puddles.

One of the most fascinating aspects of this migration is that it takes place over several generations.  The last generation of the summer hatches at the northern limit of monarch range.  That generation delays sexual maturity and, triggered by the changing season, begins the 3,000 mile journey to Mexico, where it spends the winter.  In early March these butterflies reach sexual maturity and head north, mating as they go.  Some get as far as southern Texas, where the females lay eggs and die.  The next generation hatches and, after completing metamorphosis, heads north and east and repeats the process.

Over three or four more generations, monarchs repopulate the rest of the continent easy of the Rockies, until the last generation of the season begins the southern migration again.  A similar, thought shorter, migration happens west of the Rockies as Monarchs overwintering in California head north.

Understanding the Milkweed Connection

Butterfly gardens must provide food for both adults and caterpillars.  Monarch caterpillars feed exclusively on milkweed, a double-duty plant that also serves as a nectar source for adult butterflies.  Milkweed has a sap that contains alkaloids, which make the insects taste bad to birds and other predators.  The striking coloration of the monarch evolved as a warning that tells predators, “Don’t eat me; I taste bad.”

Start your monarch garden by planting milkweed species such as swamp milkweed (Asclepias incarnata, butterfly weed (A. asperula), and common milkweed (A. syriaca).  If possible, choose a species that’s native to your region.  Plant native perennials to provide nectar from spring through fall.  Because monarchs migrate, late-season nectar is particularly important.  Good choices include coneflowers (Echinacea spp.), ironweed (Vernonia spp.), Joe Pye Weed (Eupatorium fistulosum), sedum (Sedum spp.), and verbena (Verbena spp.).  Commercial nectar is also available along with butterfly feeders specially made to provide a quick meal to migrating butterflies.

Add some dense shrubs where the butterflies can hide from hard rains and strong winds or a butterfly house Avoid insecticides, which can kill butterflies.  Then sit back and wait for these orange and black beauties to arrive.

Note: Avoiding Butterfly Bush

Butterfly bush (Baddleia spp.) has long been a staple for gardeners trying to attract butterflies, and there is no doubt that butterflies find the shrub irresistible.  An import from Asia, butterfly bush comes in many colors and grows in a variety of conditions.  Beware however, butterfly bush has become invasive in some parts of the country, notably the Pacific Northwest and Mid-Atlantic region.  Choose native perennials and flowering shrubs instead.

Click the link below for an interesting video from the New York Times.

Monarchs and Migration

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