Fewer monarch butterflies will herald spring this year
Wet and cold weather damaged their habitat
One of the sure signs of spring — monarch butterflies — might be harder to find this year, scientists announced this week.
After a significant rise last year, the number of monarch butterflies at winter breeding grounds in Mexico is down once again, says butterfly tracker Craig Wilson, a senior research associate at Texas A&M University.
Last winter, storms toppled trees and severely damaged the habitat, which coupled with cold and wet weather was “enough to kill many millions” of the colorful creatures, he says. The devastation left about 78 million monarchs in Mexico’s breeding grounds, down from 100 million a year before.
The figures illustrate the striking decline in the migrating butterflies’ population in the past two decades. Today, monarchs number less than one-tenth of their population in 1996, when scientists estimated there were 1 billion of the insects, Wilson says.
A study from the World Wildlife Fund released this month found bad weather and deforesta- tion are the top threats to migrating monarch butterflies.
Monarch populations are measured by the number of acres of trees occupied by clustering but- terflies that spend the winter in Mexico. This year, monarchs covered about 7 acres of trees, down from 10 acres last year. Two decades ago, the butterflies occupied as many as 44 acres of trees, according to Monarch Watch.
After spending winter in Mexico, the monarchs flap their way north into the USA and Canada in the spring and summer. No single butterfly finishes the entire journey; it takes a few generations to complete the trip. In the spring and summer, the monarchs live only about two to five weeks.
A final generation then migrates back south to Mexico in the fall to start the cycle again.
Declining milkweed, the monarch caterpillar’s only source of food, has hampered the insects’ 2,000-mile journey in recent years. Dwindling numbers of the plant is linked to an increase in herbicide-resistant crops, dry conditions over much of Texas and numerous wildfires.
A plentiful supply of milkweed is needed in the central U.S. for the monarch’s long-term survival, and state and local officials are urging the public to get involved, Wilson says.
Though some monarchs don’t migrate and aren’t in decline, it’s the decrease in the migrating monarchs that’s especially concerning.
Wilson says, “We need this incredible migration story to keep going.”