Waning Numbers Of Monarch Butterflies Rebound To 140 Million Insects This Winter

A couple of years ago, there weren’t too many monarch butterflies in their winter sanctuary in Mexico. In fact, their numbers were so low that conservationists feared the beautiful insects were endangered.

But this year, their numbers seem to have rebounded, raising hopes that the species is no longer threatened and on a road to recovery, Discovery reported.

However, the factors that decreased the numbers of monarch butterflies so drastically are still a threat — namely illegal logging, pesticide use, and unpredictable climate — so conservation officials are stressing that everyone must work to help the population thrive.

And helping monarch butterflies is as simple as planting milkweed.

The encouraging news about monarch butterflies comes from U.S., Mexican, and Canadian officials. They announced that the insect’s numbers spread to cover 4.01 hectares (or 9.9 acres) of pine and fir forest in Mexico this winter season, which is three times more than last year.

This equates to about 140 million monarch butterflies. Since the insects gather on the pine and fir trees so densely, scientists calculate their population in area, instead of individuals, CBS News explained.

These numbers are very encouraging compared to the winter of 2013-2014, when the population hit a sobering low of only 0.67 hectares. And while the increase is hopeful, monarch butterflies still aren’t what they used to be — 20 years ago, they covered 44 hectares.

“It’s very good news,” said Omar Vidal of Mexico’s World Wide Fund for Nature. “At the same time, we can’t lower our guard in any of the three countries and we must redouble our efforts to ensure this migratory phenomenon transcends this and the next generation.”

The migration of monarch butterflies is an incredible phenomenon. Every year, they fly 1,200 and 2,800 miles from the U.S. and Canada. By October, they arrive in Mexico, where they’ll spend the winters hibernating in a mountain reserve in Michoacán State and Mexico State. By March, monarch butterflies start the return trip back north.

The insects breed on the way, and their newly hatched babies finish the trip (no one knows how the next generation knows where to go in Mexico every year, the New York Times noted).

A key cause of the decline in their numbers is the destruction of milkweed, a critical plant for the creatures, either by use of pesticides or clearing of land. The insects need milkweed for food; they also lay their eggs on the plant.

“The widespread use of increasingly deadly pesticides is a death knell for monarch survival. We need to scale back the use of these pervasive pesticides and plant more milkweed to keep these incredible creatures alive and thriving,” said scientist Sylvia Fallon.

Last year, the U.S. Fish and Wildlife Service joined two conservation groups to protect monarch butterflies and restore their numbers. They spent $2 million to plant milkweed on 200,000 acres, focusing on the I-35 corridor from Texas to Minnesota, which is their spring and summer breeding habitat. The department’s director, Dan Ashe, said that people across that area can help by planting milkweed in their own backyards. He hopes to restore numbers to 250 million monarch butterflies by 2020.

Herbicides are still a huge problem in the U.S., so the threat hasn’t disappeared. Moreover, illegal logging in the sanctuaries hasn’t stopped, although Mexico has responded by enlisting local farmers to help keep watch over the 140,000-acre reserve that serves as their hibernation grounds.

Climate can also cause problems. Monarch butterflies and all insects are very vulnerable to changes in temperature, and threats like global warming can affect the winter habitat.

The numbers got a boost this winter, conservations said, because of new milkweed plantings, mild weather, and efforts to protect their forest. And officials, citizens, and conservationists must continue to be vigilant if they hope to completely restore monarch butterflies, said Vidal.

“The threats to the monarch remain and if they are not dealt with, if actions are not followed through, the migratory phenomenon won’t recover.”

[Image via Galyna Andrushko/Shutterstock]