As many as 300 million monarch butterflies are now flying south from Canada and the northern United States to winter in Mexico and Southern California.
But, thanks to this year's hot and dry U.S. summer, the number of monarchs has soared, the Chicago Sun-Times reported Monday.
"I counted over 100 just looking out the window while I was getting a cup of coffee," Doug Taron, curator of biology at the Chicago's Peggy Notebaert Nature Museum, told the newspaper.
This summer's hot and dry conditions were nearly perfect for the black and gold butterflies, increasing their numbers up to 10 times over last year in some area.
"It's the drought," Taron said. "Butterflies in general seem to do well in warm, dry years." He said such weather conditions eliminate many of the funguses and bacteria that usually kill the monarchs' eggs or destroy the butterflies while they are still caterpillars.
The monarch butterflies will fly more than 2,000 miles to gather at a dozen wintering areas in the mountains west of Mexico City.
Copyright 2005 by United Press International
Explore further: Rosetta comet-landing is Science's 2014 breakthrough