Econintersect: An icon of the North American continent, the Monarch butterfly, has seen a population decline of more than 96% in the past 18 years. The reason a fairly accurate measurement of the population is possible derives from the wintering location of a large portion of the species in a small forest area of Mexico, known as the Rosario Monarch Preserve. In 1996 an estimated 1 billion Monarchs covered an area of about 45 acres. This month there were about 35 million over just 1.65 acres.
El Rosario Butterfly Biosphere Reserve, 62 miles northwest of Mexico City.
The Monarch has an annual migration of 2,000 miles or more from wintering locations in Southern California, Texas, Florida and Central Mexico (the largest population) to spend summer months across the U.S. and Canada. One of the several pressures on the population, and the newest, is the major decline of milkweed plants which provide a key component of Monarchs’ diet givings them a toxicity that repels predators. The decline of milkweed, the only place that the insect will lay eggs, is attributed to more widespread use of herbicides over the past two decades.
Click on photo for larger image at Wikipedia.
Monarchs wintering near Angangueo, Michoacan, Mexico.
There are many longstanding challenges to the Monarch which have decimated the population on specific occasions. But these have often been one-time events that offered only short-term setbacks from which the population recovered. One such event was a deep freeze in Central Mexico in 2002 that killed 80% of the population. From CNN:
There are several reasons for the decline, including extreme climate events in the U.S. and Canada as well as deforestation in Mexico. Yet the biggest culprit is likely the widespread extermination of milkweed, a flowering plant critical to monarch butterfly reproduction and development.
The development of GMO (genetically modified organisms) that are resistant to herbicides (such as RoundUp) has allowed farmers to greatly increase applications of the chemical which has decimated traditional native plants such as milkweed.
Movements are underway to try to get gardeners to plant milkweed in order to restore some of the butterfly habitat.
A video just over 2 minutes long (which predates the milkweed situation) is available from The National Geographic:
While the population of Monarch butterflies in North America is by far the largest on the planet, the colorful insects are also found in Western Europe, India, Australia and on some Pacific Islands.
Hat tip to Roger Erickson.
Sources:
- North American Leaders Urged to Restore Monarch Butterfly’s Habitat (Elisabeth Malkin, The New York Times, 14 February 2014)
- Monarch Butterflies (National Geographic)
- NAFTA leaders could save the monarch butterflies (Carter Roberts and Omar Vidal, CNN, 14 February 2014)
- Butterflies, Moths: Monarch Butterflies (National Geographic Video)
- Roundup Pro Concentrate (Monasanto Corporate website)
- GEI News articles about Roundup
- GEI Opinion articles about Monsanto
