Seeds ripen as moths return

The prairie edges near Boulder hold a quiet abundance this late spring morning. Blackeyed Susan (Rudbeckia hirta) stands in scattered clusters, their dark seed heads swollen and heavy. The bright yellow petals have long since dropped, leaving behind the central cones that now bristle with ripe achenes. Each seed head looks like a small brown cushion studded with hundreds of individual seeds, ready to scatter with the next strong wind.

The Brother Moth (Raphia frater) emerges from the soil just as these seeds reach peak ripeness. This native moth spends most of its life underground as a caterpillar, feeding on grass roots through the winter months. But in late spring, the adults surface to find the prairie forbs at exactly the right moment. The moths are drawn not only to the remaining flowers of wild bergamot (Monarda fistulosa) and eastern purple coneflower (Echinacea purpurea), but to the developing seeds themselves. Their larvae will feed on the ripening seed heads, creating a partnership that has shaped both species for generations.

Nearby, the Dusky Raisin Moth (Ephestiodes gilvescentella) follows a similar rhythm. These small, gray-brown moths appear just as the wild bergamot finishes its flowering cycle. The bergamot's square stems now support clusters of brown seed capsules, each one containing four nutlets that will feed the moth's caterpillars through their development. The adult moths still visit any lingering purple coneflower blooms, their proboscis reaching deep into the spiny flower heads for nectar, but their real purpose is reproduction timed to the seed harvest. The female moths lay their eggs directly on the ripening seed heads, ensuring their young will have fresh food when they hatch.

This synchrony between seed maturation and moth emergence creates a brief but crucial window in the prairie's yearly cycle. The forbs invest tremendous energy in seed production, and the moths have evolved to exploit this resource precisely when it becomes available. The blackeyed Susan's achenes contain oils and proteins that nourish developing moth larvae, while the purple coneflower's seeds provide carbohydrates and fats. In return, the moths inadvertently disperse some seeds as they move between plants, carrying them on their bodies and in their digestive tracts to new locations. The relationship benefits both partners, even as it appears to pit them against each other.

Step outside now and look for these seed heads among the late spring growth. The blackeyed Susan's dark cones stand out against the green backdrop, each one a small monument to the season's reproductive success. If you run your fingers gently across the surface of a ripe seed head, you can feel the individual achenes, some already loose and ready to fall. Somewhere in the grass nearby, the Brother Moth rests through the day, waiting for evening to begin its search for the next cluster of seeds.