By Robert Nicholson

Sometime in late summer — usually August in Ohio — something orange begins to move.

It starts as a flicker at the edge of a meadow, a single butterfly resting on a milkweed stem. Then another. Then dozens. Then, if you are lucky enough to be near a good patch of wildflowers on a clear September morning, hundreds of monarch butterflies moving steadily southward — tiny, brilliant, improbable things making their way across a continent toward a mountain range most of them have never seen.

The monarch butterfly migration is one of the great natural spectacles on Earth. It is also one of the most threatened.

In recent decades, monarch populations have collapsed — eastern populations down 80 percent from their peak, the western population down more than 95 percent. The insect that once carpeted oyamel fir forests in Mexico by the hundreds of millions now covers a forest the size of a small backyard.

This summer, there is cautious reason for hope. But hope requires understanding — what monarchs are, where they go, why they are struggling, and what any of us can actually do about it.

Just 30 years ago, monarchs covered nearly 45 acres of forest in their Mexican wintering grounds. This past winter, they covered 7.24 acres. That is the scale of what has been lost.

The Journey: Four Generations, Three Countries, Three Thousand Miles

The monarch butterfly migration is unlike any other insect migration in the world. It is not accomplished by a single butterfly making a round trip — it is a relay race spread across four generations, each one picking up where the last left off, guided by the sun, Earth's magnetic field, and instincts encoded over millions of years of evolution.

Here is how it works:

PHASE 1 THE WINTER COLONY | November – February

Each autumn, the final generation of the year — called the Methuselah generation — flies south from the northern United States and Canada to oyamel fir forests in the mountains of central Mexico, roughly 60 miles northwest of Mexico City. At elevations above 10,000 feet, these forests maintain a narrow band of temperature and humidity that keeps the butterflies alive without burning the fat reserves they need for spring. Millions cluster so densely on tree branches that the branches bow under their weight. The forest literally turns orange.

PHASE 2 THE SPRING JOURNEY NORTH | March – May

In early spring, as temperatures warm and days lengthen, the overwintering monarchs become reproductively active for the first time. They mate and begin flying north, stopping in the southern United States to lay eggs on milkweed plants — the only plant monarch caterpillars can eat. These winter survivors die after reproducing. Their offspring, the first generation of the new year, continue the journey northward.

PHASE 3 THE SUMMER BREEDING SEASON | May – August

Through late spring and summer, monarchs spread across their breeding range — roughly the northeastern United States and southern Canada, including Ohio. Over this period, two or three generations are born, each one living only a few weeks, mating,

laying eggs, and dying. Milkweed is everything during this phase. Without it, there are no caterpillars. Without caterpillars, there are no butterflies. Without butterflies, the journey ends.

PHASE 4 THE MIGRATION GENERATION | August – November

The final generation of the year is different from all the others. Born in late summer, these butterflies enter a state called diapause — a kind of reproductive pause that redirects their energy toward fat storage and migration rather than breeding. They live six to eight months instead of the usual two to six weeks. Guided by the angle of the sun and a time-compensated compass in their antennae, they fly up to 3,000 miles to Mexican mountains they have never been to before. When they arrive, the cycle begins again.

The fact that this works at all is astonishing. No individual monarch completes the round trip. The butterfly that leaves Mexico in spring will die in Ohio. Its great-grandchildren will return to Mexico in fall — to the same mountains, often the same trees — without ever having been shown the way.

The Threats Facing Monarchs

The monarch's decline does not have a single cause. It is the result of several pressures converging over decades — each one manageable in isolation, collectively devastating.

1. The Disappearance of Milkweed

Milkweed is not optional for monarchs. It is the only plant monarch caterpillars can eat. A female monarch will not lay her eggs on anything else. Where milkweed goes, monarchs go. And over the past several decades, milkweed has been disappearing from the American landscape at a staggering rate.

The primary driver is agricultural herbicide use. Beginning in the late 1990s, the widespread adoption of genetically modified, herbicide-resistant corn and soybean crops — engineered to survive applications of glyphosate — transformed the Midwest. Farmers could spray entire fields to kill weeds without harming their crops. The result was the effective elimination of milkweed from millions of acres of agricultural land that had once supported it between crop rows.

Researchers estimate that more than a billion stems of milkweed were removed from the North Central United States alone. The Corn Belt, which had been one of the most productive monarch breeding grounds on the continent, became largely inhospitable. The monarchs that had relied on that habitat for generations found themselves with nowhere to reproduce.

Milkweed once grew abundantly between rows of corn and soybeans across the Midwest. The widespread adoption of herbicide-tolerant crops changed that, removing over a billion stems of the plant from the landscape.

2. Loss of Nectar Plants

Adult monarchs do not eat milkweed — they drink nectar from a wide variety of flowering plants. During migration, they need reliable nectar sources spaced along their route to fuel the long journey. As prairies have been converted to cropland, roadsides have been mowed more aggressively, and suburban development has replaced wildflower meadows with lawns, the nectar corridor that monarchs have used for thousands of years has become increasingly fragmented.

A butterfly that cannot refuel during migration cannot complete the journey. And a butterfly that does not complete the journey does not reproduce next spring.

3. Climate Change

Climate shifts are disrupting the timing of the migration itself. Warmer springs in the southern United States and Mexico have triggered earlier breeding seasons — sometimes before milkweed at northern latitudes has reached the right growth stage for caterpillars to feed on. This mismatch between when butterflies arrive and when their food source is ready can reduce reproductive success across an entire generation.

At the other end of the journey, the mountain forests where monarchs winter are becoming less stable. Storms, drought, and illegal logging have reduced and degraded the oyamel fir forests. A single catastrophic freeze or storm can kill millions of monarchs in a matter of hours — events that are becoming more frequent as climate patterns shift.

4. Pesticides

Neonicotinoid insecticides — widely used on crops and ornamental plants — are toxic to monarchs at all life stages. These chemicals are applied to crop seeds as coatings and are taken up into the plant's tissues, including the pollen and nectar. Monarchs that feed on contaminated flowers or whose caterpillars feed on milkweed plants growing in treated areas can be directly harmed.

Additionally, volatile herbicides sprayed on newer herbicide-resistant crops can drift to adjacent areas, reducing the wildflowers and other plant resources that monarchs rely on during migration.

Monarchs in Ohio: What to Watch for This Summer

Ohio sits squarely in the monarch's summer breeding range and fall migration corridor. From late May through August, monarchs breed across the state, with females seeking out milkweed plants to lay their eggs. By late August and September, the migration generation begins its journey southward — and Ohio is one of the best places in the Midwest to watch them pass through.

Here is what you might see and when:

• May-June: First- and second-generation monarchs arrive and begin breeding. Look for females hovering low over milkweed patches, curling the tip of their abdomen to deposit eggs on the underside of leaves.

• June-August: Caterpillars — boldly striped in yellow, black, and white — are visible on milkweed plants if you look closely. They eat voraciously and grow from a pinhead to a full caterpillar in about two weeks.

• August-September: The migration begins. Monarchs concentrate at good nectar sources and begin moving steadily southward. Patches of goldenrod, Joe Pye weed, and ironweed become temporary rest stops for dozens of butterflies at a time.

• September-October: Peak migration through Ohio. Lake Erie shorelines, particularly the Ottawa National Wildlife Refuge and Magee Marsh, can be spectacular gathering points as monarchs wait for favorable winds to continue south.

If you see a monarch in your yard this summer, you are watching one link in an unbroken chain of migration that has continued for thousands of years. It is worth stopping for. ■