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Friday, October 11, 2013

Magical Monarch Migration

Monarch male, Danaus plexippus

Most of us are aware of the typical life cycle of a butterfly – first an egg is laid on a food plant, a caterpillar (or larvae) hatches from the egg, once the caterpillar eats enough it  turns into a chrysalis, and shortly after a beautiful adult butterfly emerges.  However, unlike other butterflies, migration plays a key role in the Monarch’s lifecycle, and it is a fantastic migration at that!

Monarch caterpillar
Monarch chrysalis
Unlike most other insects in temperate climates, Monarch butterflies cannot survive a long, cold winter.  Instead, they spend the winter in one of two main roosting spots – those west of the Rockies travel to small groves of trees along the California coast, and those east of the Rockies fly further south to the forests high in the Chihuahua Mountains of Mexico.  

Butterfly Milkweed, Asclepias tuberosa
Austin is on the very eastern edge of this central flyway to Mexico, and in October/November large numbers of Monarchs work their way through Central Texas.  These butterflies were actually born on milkweed plants in Canada earlier in the summer.  Even though they look like summer adults, they won’t mate or lay eggs until the following spring.  Instead, their small bodies prepare for a strenuous flight.  As they migrate southwards, the Monarchs stop to nectar, and actually gain weight in the form of fat to fuel their flight and last them throughout their winter roost.  These butterflies wake up about mid-morning, gathering nectar from flowers in full bloom, and fly until sunset, covering distances up to 400 miles in a single day.  Although this generation of butterflies has never ventured into Mexico in the past, somehow they still find their way. 

Once they reach their wintering grounds in Mexico, the Monarchs roost in huge clusters that virtually drip off the evergreen trees, and feed on the nectar of native plants.  If they survive the winter, they will begin the trip back to Canada in late March or early April.  Although the same butterflies that winter in Mexico don’t survive long enough to see Canada once more, the next three generations carry on the lifecycle as they migrate north.  Each first through third generation lives only six to eight weeks, and it is this fourth generation -- the great, great grandchildren -- that complete the return journey back into Mexico.

Driven by seasonal changes such as temperature and day length, the migration of the Monarch is unique in all the world.  They travel up to a total of 3,000 miles -- much farther than all other tropical butterflies and they are the only butterfly species to make such a long, two-way migration every year.  Amazingly, they fly in masses to the same winter roosts, often to the exact same trees, but unlike other migrating species (such as birds and whales), it is their children’s grandchildren that return south the following fall.  

Now that you know a little something about their magical migration, stop to admire these amazing beauties as you see them flutter by you this fall on their way to their winter home in Mexico!