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Monarch Butterfly Migration Update: April 25, 2003

Today's Report Includes:

News From Along the Migration Trail

The monarchs have now advanced into 16 states, with Indiana added this week. In which states or provinces do you predict the migration will arrive next?

Fading Away, But Still Flying Northward
Again this week came reports of faded and tattered monarchs, this time in Texas, Kansas, Florida, Georgia and Tennessee. These monarchs have been alive for a long, long time!
Torn, tattered and faded, this monarch was found in late April in Arkansas by Jim Edson
Fresh new monarch wings compared to the old.
Photo by Harlen Aschen

How Long Have These Monarchs Been Alive?
During the summer breeding season, monarchs live for only 2-6 weeks. How long does the over-wintering generation live? Think back to when you came to school last fall. You may have raised your own monarchs and sent them on their way to Mexico. If your monarchs are still alive, how old would they be now?

Challenge Question #21
"Assume a butterfly emerged as an adult late last summer, on August 25th. As of today, April 25th, how long has the butterfly been alive?"

(To respond to this question, please follow the instructions below.)

Herbivores and Plants: A Co-evolutionary Arms Race
When a predator attacks, the prey runs, flies or swims to safety. What do plants do to avoid herbivores? They don't just stand there--although that's how it may appear at first glance. A closer look at plant/herbivore interactions reveals an astonishing array of defenses and counter defenses.

Monarchs and milkweed are a case in point. "A co-evolutionary arms race is operating in this plant-herbivore system," says Dr. Lincoln Brower. Let's look at both sides of the battle:

Two Milkweed Defenses: Being Sticky and Poisonous
Here are two chemicals that any potential milkweed herbivore will confront:

  • Latex: A milky white sap that becomes sticky and coagulates when exposed to air. (Latex contains particles of rubber. It is found in a variety of plants, including rubber trees.)
  • Cardiac glycoside: As the name implies, this chemical affects the heart. To various degrees, it is toxic to herbivores with hearts (birds and mammals). Monarchs and several other arthropods that eat milkweed have a tolerance for cardiac glycosides, although evidently not at the high levels found in some milkweed species.

A Counter Attack: Leaf-notching Larvae

In this video clip, watch the monarch cut the petiole of the leaf before beginning to eat it. This "leaf-notching" behavior cuts off the supply of latex. Look how careful and thorough the caterpillar is. Amazingly, he walks down the very leaf he clipped, which seems to be "dangling by a thread."

Many Don't Make It: Little Larvae Stuck in Latex
A study by Zalucki, Brower and Alonso studied the negative physical and chemical effects of latex and cardiac glycosides on first-instar monarch butterfly larvae. They found that, among other observations, 27% of the 1 instar larvae became mired in the sticky latex and died. The scientists used forceps to nibble through the petioles of milkweed leaves, mimicking the behavior of mature monarch larvae. Here are other observations from their publication:
What Does it Look Like? Form and Function in Nature

Courtesy of Dr. Lincoln Brower and Donna Williams, University of Florida

Study the photo to the right. What do you suppose this might be?

Challenge Question #22
"What do you think is shown in this picture? (Clue: It is part of a monarch butterfly.)"

(To respond to this question, please follow the instructions below.)

Next week we'll reveal the actual function of this strange monarch form.

Try This! Considering Form and Function

What familiar things look like what's shown in the photo? Make a list of all the "look-a-likes" your class can generate, and then write a poem incorporating them. Here's an example:

Mushrooms in a mass of moss
Telescopes peeking up from sea
Spaghetti noodles, crochet needles
Necks with heads caught in rubber bands

Go back through your list. Think carefully about the structure and function of each noun you named. Why are they shaped the way they are? Write a careful description of what each is and what it does.

Mystery Monarch Habitat: Challenge Question #23
The pond is no longer frozen beside this monarch habitat, located 1836 miles (2955 km) from the overwintering sites in Mexico. If a monarch flew due north from the sanctuaries, then chose the state to the east, it would be in this summer home.

Unfortunately, you can't quite read the city's name on the green highway sign in the backdrop so you'll have to guess:

Challenge Question #23
"In what state or province do you think this monarch habitat is located? Send us your guess! (And, if you like, send a photo of your local monarch habitat, along with geographical clues, for a future Challenge Question.)"

(To respond to this question, please follow the instructions below.)

How to Respond to Today's Challenge Questions:

IMPORTANT: Answer only ONE question in each e-mail message.

1. Address an e-mail message to:
2. In the Subject Line of your message write: Challenge Question # 21 (#22 or #23)
3. In the body of EACH message, give your answer to ONE of the questions above.

The Next Monarch Butterfly Migration Update Will Be Posted on May 2, 2003


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