SEPTEMBER
1992

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

9-24-92

Beautiful But Bitter

It's yellow, black and white-striped youth, has 14 leg-like appendages, fearsome mandibles and a hard-shell head.  It feeds on a plant that contains chemicals used as medicine.  Later, as an adult, it's brown with black stripes, and spends the winter in a remote mountainous region of Mexico.  Could it be an invader from outer space or a creature from the black lagoon?

Well, actually, it's the Monarch butterfly!   One of our best known insects.  The bright, striped colors of the larva warns potential predators that it's distasteful.

The bitter taste of the larva comes from the juice of the milkweed plant that it uses for food.  The milkweed plant contains bitter substances called cardiac glycosides, which are named for their use as a human heart medicine.  These compounds benefit the milkweed plant  by acting as antifeeding compounds for most animals including insects.

The Monarch, however, has developed the ability to utilize the plant in spite of the presence of the bitter chemicals.  The larva stores the toxic compounds in its body.  This makes the larva bad-tasting,, an attribute that is transferred to the adult following pupation.

Many birds are predators of insects, but they can't tolerate the bitter taste of the Monarch.  To advertise their bad taste, the Monarch, in both the adult and larval stages, wears bright colors.  So effective is the scheme that the Vicroy butterfly, a good-tasting insect which resembles the Monarch in color and pattern, also is protected.

The Monarch, actually a tropical butterfly, has adapted to more northern climates by leaving the winter behind.  Each fall Monarchs leisurely flutter toward overwintering areas in the mountains of Mexico.

Along the way, great flocks of these insects sometimes gather on trees to rest overnight.  These resting sites, called butterfly trees are on of natures truly memorable sites.

The Monarch butterfly is indeed a biological miracle.  These fragile insects wing over 1,000 miles to a place they've never been.  Come spring they head north to lay eggs on plants too toxic for most animals to eat.

Once egg laying is complete, the butterflies die, leaving the younger generation to carry on.  Each succeeding generation moves northward to lay eggs until their genetic code unerringly indicates that it's time to turn around.

The butterflies begin the long and treacherous southern journey.  They make the trip not so much for themselves, but to ensure the survival of the future generations of the “beautiful but bitter” Monarch.

 

Writer: Tom Turpin
Editor: Elaine Lambert