Monarchs and milkweed in midsummer

The air shimmers with heat over the meadows near downtown Nashville, where summer has settled into its longest days. Common milkweed stands shoulder-high in scattered patches, their broad leaves catching the morning light before the temperature climbs. Each plant holds a cluster of dusty pink flowers at its crown, releasing a sweetness that carries on the still air.

A monarch butterfly works methodically through the milkweed patch, her orange wings marked with black veins and white-spotted borders. She is not here for nectar. The female monarch tests each plant with her feet, drumming against the leaves to taste the chemistry beneath. When she finds the right plant, she curves her abdomen and places a single cream-colored egg on the underside of a young leaf. The egg is smaller than a pinhead, ribbed like a tiny melon. She moves to the next plant and repeats the process, spacing her eggs carefully across the patch.

The milkweed she chooses will be both nursery and food for her offspring. When the caterpillar hatches in three days, it will eat its own eggshell first, then begin consuming the milkweed leaf. The plant's milky sap contains cardiac glycosides, compounds toxic to most animals but harmless to monarch caterpillars. As the caterpillar feeds and grows through five molts over two weeks, these toxins accumulate in its tissues. The bright yellow, black, and white stripes that develop serve as a warning to predators: this caterpillar tastes terrible and could make you sick.

The milkweed tolerates this relationship. A single plant can support several caterpillars without significant damage, and the adult monarchs that emerge will visit other milkweed patches for nectar, carrying pollen between plants. The monarch's dependence runs deeper than convenience. No other plant can substitute for milkweed in the caterpillar's diet. Without milkweed, there are no monarchs. In Nashville's urban landscape, where development fragments natural areas, these patches of common milkweed become islands of possibility. The female monarch may have traveled miles to find this stand, following chemical cues and visual landmarks that guide her to the plants her species requires. Her eggs represent the continuation of a journey that began in Mexico and will end in Canada, carried forward by successive generations that live and die without seeing the same landscape twice.

The milkweed flowers release their fragrance strongest in the early morning, before the heat builds and the air grows still. If you find yourself near a patch like this one, notice how the sweetness carries just a few feet before dissipating, drawing you closer to see what the monarchs have found.