Monarch Butterfly Migration Update: April 25,
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!
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?
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:
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
Study the photo to the right. What do you suppose this might be?
Next week we'll reveal the actual function of this strange monarch form.
Try This! Considering Form and Function
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:
How to Respond to Today's Challenge Questions:
1. Address an e-mail message to: firstname.lastname@example.org
Copyright 2003 Journey
North. All Rights Reserved.