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Why are Monarch butterflies disappearing?

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As kids, we're all taught about the Monarch butterfly. It is perhaps the best known of all North American butterflies.

But could you imagine a world without them? 

While above average rainfall in the U.S. this year has increased the number butterflies, the Monarch butterfly population continues to decline.

“The Monarch population last year was estimated to be at 60 million versus 350 million just a few years earlier -- so it’s a dramatic change,” said Dr. Gene Kritsky, professor of biology at the College of Mount St. Joseph.

Entomologists, like Kritsky, are concerned about the Monarchs and their sudden decrease in numbers.

Kritsky called the decline in Monarchs an “alarming event.”

“A world without Monarchs is kind of sad,” he said. “It’s one of the first butterflies that kids learn to recognize.”

So why are the Monarchs disappearing?

Illegal logging in the reserve established in the Monarch wintering grounds was long thought to contribute, but such logging has been vastly reduced by increased protection, enforcement and alternative development programs in Mexico.

However, the World Wildlife Fund, one of the groups that sponsored the butterfly census, blames climate conditions and agricultural practices, especially the use of pesticides that kill off the Monarchs' main food source, milkweed.

The butterflies breed and live in the north in the summer, and migrate to Mexico in the winter.

“The decline of the monarch seems to be related to the increased use of genetically modified corn and soybeans which is modified to allow them to withstand exposure to herbicides,” said Kritsky. “They can now use herbicides and keep their fields clean of milkweed, which is one of the major weeds you’ll find in corn and soybeans and that’s the food source for the Monarchs.”

The loss of milkweed in the Monarchs' summering areas in the north can make it hard for the butterflies to lay eggs, and for the offspring that do hatch to find enough food to grow to maturity. In addition, unusually hot or dry weather can kill eggs, meaning fewer adult butterflies. For butterflies that reach adulthood, unusual cold, lack of water or tree cover in Mexico can mean they're less likely to survive the winter.

You can help increase the Monarch population by planting more “butterfly-friendly” plants in your garden, or build a butterfly garden, experts said.

“If you’re going to do your own butterfly garden, you need to have a sunny location and preferably about five to six hours of good sun, not windy. And then you want to pick things that are very colorful,” said Mike Brooks, assistant grower at Fort Thomas Florist and Greenhouses.

The best thing you can plant in your garden to help Monarchs is milkweed, or butterfly weed.

The Associated Press contributed to this report

Copyright 2013 Scripps Media, Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

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