measuring Monarchs.

A monarch butterfly sipping nectar from yellow goldenrod flowers in late summer.

Every fall, Monarch butterflies across eastern North America travel thousands of miles to spend the winter in the mountaintop forests of central Mexico. They cluster by the hundreds in oyamel fir trees, waiting for early spring when they’ll begin the journey back to our region. For the past two decades, scientists in Mexico have estimated the population of Monarchs overwintering there by measuring the acres of trees occupied by the butterflies.

Last winter, the population of winter Monarchs in Mexico occupied about 4.4 acres, double the area of the previous year, giving hope for this beloved pollinator that has faced decades of decline. Experts believe the surge in numbers was due to favorable weather conditions during fall migration, unlike the previous couple of years when there were extended droughts and major storm events.

But, before we start to celebrate this nearly 100 percent increase, scientists believe 15 acres of roosting Monarchs is needed for the population to stabilize. While planting native milkweed species—the only plants on which adult Monarchs lay eggs and larval Monarchs feed—is critical, it’s only a part of the complex puzzle of this species’ survival.

avoid captive rearing.

One recent study, which aggregated about 2,600 community scientists’ observation of Monarch “roosts” along the fall migration route, showed that roost sizes declined from north to south along the flyway. These data show the roosts in Texas are about 80 percent smaller than they were 17 years ago. This indicates an issue during migration.

While experts don’t fully agree on the reasons for this decline, many point to a dramatic increase in captive-bred Monarchs. On the face of it, rearing Monarch caterpillars in predator-proof enclosures seems like a great way to help the species. Yet, captive breeding—which has increased apace with concern for the threatened species—can negatively impact overall species health. It can spread disease, reduce genetic diversity, and create competition for limited resources. Several studies have shown that captive-bred Monarchs have lower survival rates.

plant only native milkweed.

A little protozoan parasite, Ophryocystes elektroscirrha or OE for short, is causing big problems for these imperiled pollinators. High OE levels in adult Monarchs have been linked to lower migration success as well as reduced lifespan, mating success, and flight ability. The parasite travels with Monarchs, and, as they sip on milkweed flowers, the butterflies inadvertently deposit it on the plants’ leaves. When caterpillars hatch and feed on the tainted foliage, they ingest the OE.

When native milkweed species die back, the parasite dies along with them. However, non-native tropical milkweed (Asclepias curassavica) remains evergreen through winter, allowing OE levels to increase year over year. Additionally, emerging research suggests that tropical milkweed may become toxic to caterpillars when the plants experience the warmer temperatures associated with climate change.

As a way to help feed Monarchs, more and more people have been planting tropical milkweed. Ironically, much like captive breeding, well-meaning people are contributing to the butterfly’s challenges.

plant lots of natives, in addition to milkweed.

Native milkweed species—which include common milkweed (Asclepias syriaca), swamp milkweed (Asclepias incarnata), butterfly weed (Asclepias tuberosa), and poke milkweed (Asclepias exaltata)—are essential for Monarch caterpillars. In fact, milkweed is the only species of plant the caterpillars can eat. It is also a great source of nectar for all pollinators.

But milkweed alone is not enough for adult butterflies. Planting a diversity of summer- and fall-flowering native plants ensures there are food sources throughout the adult stage of their life cycle. This not only helps Monarchs, but also beneficial native bees, wasps, and flies. Top choices include goldenrods, coreopsis, monarda, purple coneflower, Joe Pye weed, asters, phlox, and ironweed.

“At Stoneleigh, we’ve observed a few nectar superstars that draw an impressive number of pollinators, including wild mint (Mentha arvensis), anise hyssop (Agastache foeniculum), showy goldenrod (Solidago speciosa), clustered mountain mint (Pycnanthemum muticum), and aromatic aster (Symphyotrichum oblongifolium),” said Ethan Kauffman, director of Stoneleigh: a natural garden. “These plants enrich biodiversity and are incredibly beautiful—great additions to any yard, garden, or container.”

add your observations.

The International Monarch Monitoring Blitz is a call to action for anyone interested in the species’ conservation to contribute to community science conservation efforts. The information collected by thousands of volunteers each year helps researchers assess population trends. For example, gathering data on the number of both Monarch caterpillars and milkweed plants allows for the calculation of a “cat”-to-milkweed ratio. Researchers use this ratio to estimate the size of the Monarch population.

continue to support conservation.

By supporting Natural Lands with your membership, you help Monarchs and other pollinators. The land conservation and stewardship work that is core to Natural Lands’ mission ensures native species have access to flower-filled meadows, clean water, and biodiverse flyways.

Your financial contribution also underwrites engagement programs that introduce children and adults to butterflies, moths, and other insects as well as conservation concepts. By providing impactful experiences with the wonders of nature, you help cultivate future generations of caring conservationists.

counting winged things.

A fifth (22 percent) of U.S. butterflies have disappeared since 2000. About 33 percent of species underwent “significant shrinkage” in populations.

The study, published in the journal Science this past spring, combined data from 76,000 surveys including those by community scientists. Of the 554 species included, the scientists had enough data to make conclusions about 342 species. Their results revealed 13 times more species declined than increased, with 107 species losing at least half of their populations.

For the past three decades, volunteers and staff at Mariton Wildlife Sanctuary have been counting butterflies as a way to evaluate species populations and biodiversity. The participants count an average of 17 different species per year at our Easton, PA, nature preserve.

“There are some species that were noted in years past that are now absent, but we’ve also seen new species show up,” said Zane Miller, preserve manager.

“For example, last year was a huge year for Huron Sachem, a southeastern U.S. species that migrates north each year. They seem to be expanding their northerly range due to climate change. Red-banded Hairstreaks are another southern species that have started showing up more frequently in recent years.”

The Mariton community scientists have noted a steep decline in Monarch butterflies that correlates with regional observations.

“Observers counted only two Monarchs in 2015,” Zane said.

“But the past couple of years have been more hopeful. This past summer, we recorded 20 of them. Maybe the attention this poster-child pollinator has received in recent years—and the increase in milkweed many folks are planting in their yards—is helping turn the tide for Monarchs.”