Where Have All the Monarch Butterflies Gone?

An adult monarch flits among summer wildflower blooms in Madison, Wisconsin. Richard Hurd/Flickr

While the plight of the honeybee has launched countless efforts to save that insect in recent years, another important pollinator — one that's actually native to North America — has also suffered a dramatic population decline lately, often without generating as much buzz among gardeners and do-gooders.

The number of monarch butterflies that reach their wintering habitat in Mexico has been in decline for two decades, and fell to a record low in the winter of 2013-2014. Experts were cautiously optimistic after a slight rebound last winter, but now early indications from the 2016 migration suggest the iconic insects are still in trouble.

The full picture won't emerge until monarchs reconvene in Mexico, but thanks to monitoring programs around the U.S., scientists can start to estimate the outcome while the butterflies are still en route. And as Ted Gregory reports in the Chicago Tribune, sparse sightings have been reported so far this year in Illinois and other parts of the country. That seems to support concerns that long-term threats like habitat loss and pesticide use have been worsened this year by bad weather.

"The problem is real," renowned monarch expert Karen Oberhauser tells the Tribune. "We're seeing much, much lower than the long-term averages."

What's causing the monarch butterfly decline?

For years, experts have linked the decline of monarch butterflies to illegal logging in Mexico's oyamel fir forests, where the insects travel every winter. Habitat loss remains a concern throughout their range, although recent conservation efforts have reduced the threat of deforestation in their Mexican refuge.

Close up of monarch wing

"It is now necessary for the United States and Canada to do their part and protect the butterflies' habitat in their territories," Omar Vidal, the World Wildlife Fund director in Mexico, told the Associated Press in 2013.

As with honeybees, experts point to American farmland, which is increasingly planted with genetically modified soybean and corn engineered to withstand herbicide applications. These herbicides are wiping out milkweeds, the only plant on which monarch caterpillars feed, in critical breeding grounds in the American Midwest.

"That habitat is virtually gone. We've lost well over 120 million acres, and probably closer to 150 million acres," said Chip Taylor, director of the conservation group Monarch Watch, in a 2013 interview with the New York Times.

Milkweed loss and insecticide exposure are serious threats, but they're not the only ones monarchs face. Even without humans altering their habitats, the butterflies' numbers fluctuate from year to year based on variables like weather and disease. Severe storms can wreak havoc with the fragile insects, while droughts may leave them too weak to finish their epic, 2,500-mile migration.

The 2010-2013 Texas drought, for example, has been cited as a likely factor in the 2013 decline, since that state is a key part of monarchs' yearly journey. And in 2016, the apparent drop could also be linked to extreme weather, experts say. An intense storm hit the butterflies' Mexican forest refuge in March, Oberhauser notes, which has already been diminished by deforestation. The storm not only killed large numbers of wintering monarchs, but also damaged many of the oyamel trees on which they depend. Plus, Gregory reports, a long period of cold, wet weather around Chicago may have contributed to fewer sightings in Illinois this year, since those conditions favor bacteria and fungi that plague monarch larvae.

Any further decline of monarch butterflies should alarm us. While it won't mean a death blow in the immediate future for one of the world's great migrations, it does make monarchs even more vulnerable than they already are.

How you can help monarch butterflies bounce back

monarch butterfly migration map
This map depicts monarchs' spring ranges in green, summer in yellow and fall in orange. Click to enlarge. (Photo: FWS)

This map shows monarchs' spring migration in green and fall migration in orange. Click to enlarge. (Image: FWS)

While officials are busy assigning blame for the decline, there is something the rest of us can do that will help boost numbers.

Start by planting milkweeds if you live along the monarch migration path. Monarch Watch has a list of shrubs, cultivated annuals, perennials and wildflowers that make good nectar sources for butterflies and can help create a butterfly garden.

In particular, create a mud puddle to provide male butterflies with the minerals they need to reproduce. Butterfly Pavilion recommends home gardeners sink a pan into the ground that is filled with equal parts sand and composted manure. If kept moist throughout the growing season, the puddle may become a gathering place for butterflies.

Before placing your fruit scraps into the compost bin, toss the chunks of rotting apples, pears, peaches, and oranges into a mesh bag and hang them from a tree for butterflies.

While there is little we can do about the expansion of farmland destroying feeding grounds for monarchs, we can take small steps that will have a big impact in protecting the monarch migration for generations to come.

Inset photo of wing detail: Burnt Umber/Flickr