Milkweed blooms and monarch arrival

The scent reaches you before you see the flowers. Sweet and heavy, it drifts across the Potomac parklands where common milkweed stands have begun their late spring bloom. Each cluster holds dozens of small pink flowers, waxy and intricate, built like tiny crowns. The butterfly milkweed opens beside it, its orange blooms more vivid against the green June grass.

This is the signal the monarchs have been following north. After wintering in the mountains of central Mexico, the great-great-grandchildren of last fall's migrants arrive here now, drawn by the milkweed's perfume. The timing is precise. Milkweed nectar fuels the female monarchs as they search for places to lay their eggs. Only milkweed will do. The monarch caterpillars cannot survive on any other plant.

The relationship runs deeper than food. Milkweed contains cardiac glycosides, compounds that make the plant bitter and toxic to most animals. But monarchs have evolved to not only tolerate these chemicals but to concentrate them in their bodies. A monarch caterpillar feeding on milkweed becomes poisonous to birds. The bright orange and black wings of the adult butterfly advertise this toxicity. Predators learn quickly to avoid them.

Common milkweed spreads through underground runners, forming colonies that can persist for decades. Each plant in a stand is likely connected to the others, sharing resources through their root system. When a monarch finds one blooming milkweed plant, she often finds many. The female tests each leaf with her antennae and front legs, tasting for the right chemistry before depositing a single white egg on the underside. She may lay five hundred eggs over her lifetime, but never more than one per plant. This spacing ensures that when the caterpillars hatch, they will not compete with siblings for food.

The butterfly milkweed grows differently. It forms single plants rather than colonies, its taproot reaching deep into the soil. Its orange flowers bloom slightly later than the pink common milkweed, extending the nectar season. Both species flower for weeks, their blooms overlapping with the peak arrival of monarchs in the Potomac region. This is the generation that will produce the long-lived butterflies of late summer, the ones that will fly back to Mexico in the fall.

Other insects visit the milkweed flowers too. Bees work the blooms for nectar, sometimes getting their legs caught in the flower's intricate pollen-trapping mechanism. Milkweed beetles, red and black like miniature monarchs, feed on the leaves and flowers. But none of these relationships carries the evolutionary weight of the monarch connection. The butterfly and the plant have shaped each other over thousands of years.

You can see this partnership forming now in any patch of blooming milkweed. The monarch hovers over the flower cluster, her wings catching the morning light. She extends her proboscis deep into each small bloom, taking nectar while her body picks up pollen. When she flies to the next plant, she carries genetic material between the milkweed colonies, helping to maintain the plant's diversity across the landscape.

The air warms as the sun climbs higher. Somewhere in the canopy above, a gray catbird calls from its nest. The milkweed flowers release their fragrance more strongly in the heat, and if you stand still among the blooms, you might see the next monarch arrive, following that ancient chemical conversation between flower and butterfly across the wide June sky.