The population of monarch butterflies has seen a serious decline.

Loggers have destroyed most of the migrating butterflies' winter forest habitat in Mexico. Climate change has almost wiped out wilkweed, the monarch's primary food source, USA Today reported.

Brooke Beebe, former director of the Native Plant Center at Westchester Community College usually collects caterpillar eggs and raises the winged insects into adulthood.

"I do that when they're here. They're not here," she told USA Today.

Last winter, the population of butterflies in their usual hibernating spot was the lowest it had been in 20 years.

During the 2012 to 2013 winter months, the butterflies only covered about three acres of the Mexican forest.  Twenty years ago the monarch's spread out through 45 acres.

"The monarch population is pretty strong, except it's not as strong as it used to be and we find out it keeps getting smaller and smaller," Travis Brady, the education director at the Greenburgh Nature Center, said.

Marianna T. Wright, executive director of the National Butterfly Center, said the low populations should be addressed, but should not be a cause of panic.

"It should certainly get some attention," Wright said. "I do think the disappearance of milkweed nationwide needs to be addressed. If you want to have monarchs, you have to have milkweed."

Milkweed plays an important role in monarch development , the insects lay their eggs in the plant and the caterpillars rely on it for food.

"Many people know milkweed, and many people like it," Brady said."And a lot of people actively try to destroy it. The health of the monarch population is solely dependent on the milkweed plant."

Herbicide-resistant corn and soybeans have taken over a large area of the milkweed's habitat, which is another factor contributing to its loss.

Recent natural events, such have drought and wildfires have made the butterflies' survival even more difficult.