Monarchs find their milkweed in summer heat

The heat shimmers above the pavement near downtown Oklahoma City, but step into Lincoln Train Forest and the air settles into something cooler. Here, between the urban corridors and pocket parks, milkweed plants stand tall in the longest light of summer, their clusters of small flowers drawing visitors from across the neighborhood and beyond.

A monarch butterfly works methodically along a milkweed stem, her orange and black wings catching the afternoon sun. She pauses at each leaf, curling her abdomen beneath to press a single white egg against the underside. The egg, no larger than a pinhead, carries the future of her lineage. This threatened species has traveled hundreds of miles to reach these exact plants, following an ancient map written in scent and instinct. The milkweed she chooses will be both nursery and first meal for the caterpillar that emerges in three days.

The relationship runs deeper than food. Milkweed sap contains cardiac glycosides, bitter compounds that make monarch caterpillars toxic to most predators. The caterpillars store these chemicals in their bodies, carrying the protection through metamorphosis into their adult wings. A bird that tries to eat a monarch learns quickly to avoid the distinctive orange pattern. But this chemical shield comes with constraints. Monarch caterpillars can digest only milkweed leaves; no other plant will sustain them. The adult female must find the right species, in the right condition, at the right time. Too young, and the leaves lack sufficient nutrition. Too old, and they become tough and difficult to chew.

In the urban landscape around Oklahoma City, several milkweed species bloom through summer's peak. Common milkweed spreads in colonies along fence lines and abandoned lots. Antelope horn milkweed, with its distinctive white and green flowers, thrives in the sandy soils of disturbed areas. Green milkweed grows shorter and more compact, often overlooked in the grass. Each species offers slightly different timing and chemistry, extending the breeding season and providing options as conditions change. The monarch female tests each plant by drumming her front legs against the leaves, reading chemical signatures that tell her about the plant's health and defensive chemistry. Some milkweeds concentrate their toxins more heavily; others grow more tender leaves. She chooses accordingly.

The invasive western honey bee also visits these milkweed flowers, collecting nectar alongside the threatened American bumble bee. The bees take what they need and move on, but the monarch's connection runs generational. Her caterpillars will emerge into a world where milkweed habitat continues to shrink, where herbicides eliminate the weedy spaces where these plants naturally establish, where development fragments the corridors they follow. Yet here in this pocket of urban green space, the ancient partnership continues. The milkweed grows thick and healthy in the summer heat, its flowers opening in sequence to provide nectar through the longest days. The monarch finds what she needs and leaves behind the next generation.

The afternoon light slants lower now through the trees, and somewhere in the canopy above, a great crested flycatcher calls. The monarch has moved to another milkweed plant, still searching, still testing leaves with her feet, still following the map that brought her here to this exact place in the heart of the city.