Frigates of the Air


October 22, 1991|By BARBARA TUFTY

WASHINGTON. — Washington -- The wind blows fair for Mexico this autumn day. Slipping down the coast like a tide from Canada, it flows at 15 knots an hour, bringing cool air and those frigates of the air -- the monarch butterflies.

By the hundreds of millions, these pumpkin-orange and black insects drift down through meadows, gardens, and marshes of North America, heading south on a journey as long as 2,500 miles. They fly singly or in groups, on a seemingly casual flight pattern, but constantly drifting southward as they browse from lupines to tickseed sunflowers to bur marigolds. Look up into the sky some sunlit afternoon and you might see a river of these brilliant insects, Danas plexipps, flapping, soaring, streaming south.

It's a great year for monarchs, says Dr. Douglas Sutherland of the Entomological Society of America, who is backing a federal bill to protect them and make them the U.S. national insect.

Along the east coast and as far west as the Rocky Mountains, the Danas are heading for a small valley in the Sierra Madre, west of Mexico City. There they fold their wings and drowse away the winter among the firs and pines some 10,000 feet above sea level. For ages, until 1974, this wintering spot was a mystery -- no one knew where they went. West of the Rockies, monarchs fly toward the coastal sanctuaries from north of San Francisco to Los Angeles, where the moist eucalyptus groves protect them from the cold sea winds.

This species is the only migrating species in the family that is found throughout the tropical regions of the world. Like migrating birds, they fly north to exploit the summer supply of food and then retreat back from winter to a frost-free territory. They become torpid and unable to fly when temperatures drop below 51 degrees Fahrenheit.

In spring, they will start their journey north, following the milkweed path, laying eggs on one of the 108 milkweed species throughout North America. The egg hatches into a striped caterpillar that devours the milkweed leaves, ingesting the bitter toxic chemical, cardiac glycosides, which makes them so distasteful to most birds.

In two weeks the caterpillars change through five larval stages and metamorphose into chrysalids -- jade green pendants encircled with dots of gold, fit for a queen's necklace. One week later, its cells reorganize into the wings and body of the adult monarch which then splits open the dry skin and burst out. Spreading its wings to catch the sun and pump fluid into them, in a few hours the new monarch lifts into the air.

During the summer voyage, a new generation emerges about every four or five weeks -- the life span of a summer monarch. In autumn, the great-great-grandchildren may live ten times as long -- long enough for each individual to travel south, hibernate for the winter and start northward again in spring -- a lifespan from July or August to March or April.

What an incredible journey! Weighing only a fraction of an ounce, this fragile-winged insect may encounter winds and storms that blow it off course, predators, insecticides, speeding cars and dwindling habitats. Yet feeding on nectar and buoyed by tailwinds and thermals, many arrive at the winter quarters in seemingly mint condition, even fatter than their ancestors were at the start of the journey.

It's still a mystery how they find their way to the small mountain groves they've never seen before. We don't yet know their navigation secret, or how their pinhead brains are genetically programmed.

All we can do is cheer them on as they briefly brighten our lives and lift over the fence, heading south.

Barbara Tufty is a conservation writer and editor.

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