SEPTEMBER
1989

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

9-28-89

Southward Bound

The autumnal equinox is the official beginning of fall. 'Tis the season when pumpkins sometimes wear a mantle of frost in early morning. When the fading green of the leaves of summer expose bright but fleeting hues of red and gold.

Fall is a time of harvest and quiet beauty. Mother Nature removes her summer foot from the accelerator and life begins to coast. Slowly at first, then more rapidly, earth's life cascades toward the barrenness of winter.

Fall is a harbinger of death to many of the insect world, but this is not so for the Monarch butterfly. One of the best known of North American insects, it avoids winter by migration. As fall approaches, the adult butterflies begin a truly miraculous journey to their overwintering sites.

Mountainous areas in Mexico and California provide the ideal environment for these travelers to survive the winter. Presently, only two major sites have been identified by entomologists as meeting the Monarch's requirements. In fact, because deforestation endangered one of these butterfly spas, Mexico declared it a protected area.

As these insects travel south, they create major excitement when they stop to spend the night and congregate on a single tree. These trees, sometimes called butterfly trees, are the insect equivalent of a Holiday Inn. Once at the overwintering site, the marvelous Monarch feeds on nectar from flowers to build up energy reserves for a return flight.

As spring approaches, the overwintered Monarchs begin to wing northward, as their ancestors have done for untold centuries before. During the spring journey, they mate and lay eggs on milkweed plants, a rather inhospitable host.

The milkweed plant contains compounds called cardiac glycosides -chemicals put there by the plant to keep animals from feeding on it. Most animals, that is, but not the Monarch. These insects just store the bitter substances in their bodies. As a result, they acquire a bitter taste, and consequently, insect predators, such as birds, learn quickly to avoid making a meal of the bad-tasting insect.

But bad taste alone is not enough to protect against becoming the main course for some hungry insect eater. So the Monarch wears a bright coat -one that we delight in seeing -- that is easily recognized by potential predators. In the insect world, a little catchy advertising pays dividends.

Monarch butterflies fluttering lazily in a southerly direction across an October meadow gives one pause for thought. That rather fragile insect with thin membrane wings covered with soft scales is in the middle of a journey that can cover up to 2,000 miles before it ends. It is on a journey to a location where it has never been, but to which it is unerringly guided by some genetic code.

It is truly a miracle of the biological world.

 

Writer: Tom Turpin
Editor: Carol McGrew