Monarch massacre: freak winter storms, illegal logging, suburban sprawl, widespread pesticide usecan the monarch butterfly survive? – Biology/Migration
INSECTS UNDER SEIGE
LAST JANUARY, a monster winter storm pelted four inches of icy rain over central Mexico, home to two of the world’s largest winter hibernation (resting state) sites for monarch butterflies. In the storm’s wake, frigid cold–the region’s lowest temperatures in 25 years–froze to death more than 250 million butterflies, Their rigid bodies dropped like icicles from towering tree roosts, piling up a foot high. With up to 80 percent of their colonies destroyed, it may be the largest known monarch die-off ever.
But the big chill wasn’t the only killer: Years of illegal logging added to the devastation by already having shrunk the forest’s roof. “The forest canopy was too thin to protect the delicate monarchs from bitter weather,” says butterfly expert Lincoln Brower of Sweet Briar College in Sweet Briar, Va.
With monarch numbers now alarmingly low, scientists worry the beautiful insects may be less able to rebound from future crises when they return to spring and summer breeding grounds in the U.S. and southern Canada. “A summer drought, for example, could be catastrophic,” says butterfly biologist Karen Oberhauser at the University of Minnesota.
A Mexican winter vacation may sound glamorous, but most monarch butterflies lead a brief, arduous life. In fact, millions of monarchs hatched each year in the U.S. or Canada never leave home. Instead, they spend their entire adult lives reproducing–a process so taxing they survive only two to six weeks of adulthood.
The monarch begins its life as an egg no bigger than a speck of dust. Within days, a larva, or caterpillar, emerges from the egg and immediately begins to gorge on milkweed, its sole food source. After two weeks, it swells to 2,000 times its birth weight and measures about 5 centimeters (2 inches) long. Once mature, the insect then undergoes a spectacular metamorphosis, or body change, shedding its skin, legs, mouth, and antennae. What remains: a silken sac called a chrysalis, or pupa, that 8 to 12 days later splits open to release an extraordinary black and orange-winged butterfly.
But monarchs hatched in late summer or early fall are remarkably different than those born in early spring and summer. Shorter days and decreasing temperatures signal them to forgo reproduction and instead embark on a 3,000-mile journey to the mountains of Michoacan, Mexico, where they spend eight months hibernating. Why? Like all insects, the monarch is cold-blooded: External air temperature determines its body temperature. “Monarchs are basically a tropical insect,” says Oberhauser.
Their flight is perhaps the most baffling insect migration known to scientists. In a single day, the monarch can cover 129 kilometers (80 mines), reaching speeds up to 32 km (20 mi) per hour on wings that span only 8 to 10 cm (3 to 4 in.)! Scientists call the remarkable journey an “endangered biological phenomenon”: Should the monarchs perish, so would the secrets to their mysterious migration.
Monarchs’ biggest threat is human activity. Illegal logging has destroyed nearly half the forestry within the Mexican sanctuaries, according to the World Wildlife Fund (WWF). Although illegal logging can fetch a six-year prison sentence, local farmers depend on lumber for income. One possible solution: In 2000, WWF began hiring farmers to guard the preserves rather than log them.
But preserving the monarchs’ overwintering sites is half the battle–they face habitat loss in the U.S. and Canada as well. Increasing urban development is devouring land once home to milkweed–a staple Without which they starve, Farmers’ increased use of milkweed–killing pesticides also gravely threatens their food supply. Will monarchs survive? “As long as humans don’t destroy their habitats,” says Oberhauser.
MASTERS OF MIGRATION
Thanks to years of research and help from thousands of volunteers, scientists have tracked the mysterious migration patterns of North American monarch butterflies. This map shows monarchs’ spring migration from overwintering sites in Mexico to northern breeding grounds in the U.S. and Canada. Each fall, the migration is reversed when monarchs east of the Rocky Mountains fly up to 4,828 km (3,000 mi) to the same small region in Mexico for eight months of hibernation.
Scientists still have more to learn about monarch migration and breeding–and they need your help to do it! That’s why the University of Minnesota has launched the Monarch Larva Monitoring Project, a citizen science project involving volunteers from across the U.S. To learn how you can take part, check out the Web site: www.mlmp.org
ALL IN THE FAMILY
NORTH AMERICA’S 700 BUTTERFLY SPECIES CAN BE GROUPED INTO FIVE MAJOR FAMILIES.
FAMILY NAME: Nymphalidae
COMMON NAME: Brush-footed butterflies
FAMOUS FAMILY MEMBERS: Monarch, emperor, and queen
DEFINE FEATURES: Two shortened front legs not used for flying
FAMILY NAME: Hesperiidae
COMMON NAME: Skippers
FAMOUS FAMILY MEMBERS: Brazilian skipper
DEFINE FEATURES: Big heads, wide spaced antennae; forewings fold over back when resting
FAMILY NAME: Papilionidae
COMMON NAME: Swallowtails
FAMOUS FAMILY MEMBERS: Two-tailed swallowtail
DEFINE FEATURES: Large and colorful wings; head-shaped projections on tail wings confuse predators; powerful fliers
FAMILY NAME: Pieridae
COMMON NAME: Whites, sulfurs, or orangetips
FAMOUS FAMILY MEMBERS: Cabbage butterfly
DEFINE FEATURES: Body and wings are mostly white, yellow, or orange–bright colors formed by waste products that build up in their scales.
FAMILY NAME: Lycaenidae
COMMON NAME: Gossamer-winged butterflies, harvesters, coppers, hairstreaks, blues
FAMOUS FAMILY MEMBERS: Silver-studded blue
DEFINE FEATURES: Small bodies with delicate wings, often blue in color; 40 percent of all butterflies belong to this family
Did You Know?
* During winter hibernation, the monarch butterfly is said to be in a state of reproductive diapause. The development of its reproductive organs are put on hold until the spring when warmer weather signals them to mature.
* Unlike the leaf butterfly, whose camouflaged wings blend in with its surroundings, the monarch isn’t afraid to stand out with bright orange wings. Why? Thanks to a steady diet of milkweed chemicals called cardenolides, its wings are poisonous to many predators.
* Like all insects, the monarch comes equipped with six legs, a head, thorax, and abdomen.
History: In 1935, entomologist (insect scientist) Fred A. Urquhart launched the Great Butterfly Hunt, a massive research project to track the migratory patterns of monarch butterflies. Investigate his project and write a report on his findings.
National Science Education Standards
Grades 5-8: reproduction and heredity * regulation and behavior * diversity and adaptations of organisms * natural hazards
Grades 9-12: interdependence of organisms * behavior of organisms * science and technology in local, national, and global challenges
The Great Butterfly Hunt: The Mystery of the Migrating Monarchs by Ethan Herberman, Simon & Schuster, 1990 Golden Guide’s Butterflies and Moths by Robert T. Mitchell, St. Martin’s Press, 1990
University of Minnesota’s Web site: Monarch Lab: Exploring Monarch Butterfly Biology at www.monarchlab.umn.edu
University of Kansas Entomology Program Web site: Monarch Watch at www.monarchwatch.org
CHECK FOR UNDERSTANDING
Directions: Answer the following questions in complete sentences.
1. Describe the monarch’s growth stages from egg to butterfly. Include the definition of the following vocabulary words: larva, metamorphosis, chrysalis.
2. Not all monarch butterflies migrate to Mexico. Why?
3. Cite three factors threatening monarch butterflies.
1. The monarch begins its life as an egg no bigger than a speck of dust. Within days, a larva, or caterpillar emerges from the egg and immediately begins to gorge on milkweed, its sole food source. After two weeks, it swells to 2,000 times its birth weight and measures about 5 centimeters (2 inches) long. Once mature, the insect undergoes metamorphosis, or physical and structural change, shedding its skin, legs, mouth, and antennae. What remains: a silken sac called a chrysalis, or pupa, that one week later, splits open to release a black and orange-winged butterfly.
2. Monarch butterflies are cold-blooded. The ones born in early spring and summer in the U.S. or Canada never leave home. But monarchs hatched in late summer or early fall can’t survive the decreasing temperatures. They embark on a grueling 3,000-mile epic journey to the volcanic mountains of Michoacan, Mexico, where they spend eight months hibernating.
3. (1) Illegal logging has destroyed nearly half the forestry within the Mexican butterfly sanctuaries. (2) Increasing urban development in the U.S. and Canada is devouring land once home to milkweed–the butterfly’s main food source. (3) Farmers’ increased use of milkweed-killing pesticides also gravely threatens their food supply.
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