Butterfly milkweed opens for the hairstreak
June 30, 2026
The butterfly milkweed is in flower along the open slopes near Boulder right now, its flat-topped clusters of small orange blooms catching the full length of early summer light. This is one of the drier-adapted milkweeds, rooted in rocky or sandy soils where other forbs thin out, and it holds its flowers open for weeks. If you are standing near a patch, look closely at the blooms. Something small and green may be working across them.The western green hairstreak is one of the more easily overlooked butterflies in this landscape. It has a wingspan just over an inch, and when it closes its wings, the undersides show a flat, dusty green that disappears against lichen-covered rock or leaf litter. The upperside is a plain gray-brown. It is not a butterfly that announces itself. What draws attention, if anything, is the quick, low flight between plants, and the way it pauses to probe individual flowers. This is a threatened species in Colorado, present in low numbers across its range, and the population near Boulder is one of the places it still reliably appears. Its presence here in early summer is not incidental. The butterfly milkweed is part of why it is here.Female western green hairstreaks lay their eggs directly on milkweed plants, and butterfly milkweed is one of their primary host plants along the Front Range. The eggs are tiny, flattened discs pressed against the stem or the base of a flower cluster. When the caterpillars hatch, they feed on the plant's flowers and developing seed pods. This is a narrow dependency. The hairstreak is not a generalist that will switch to another host if milkweed is scarce; it needs this plant, at this stage of flowering, to complete a generation. The early summer bloom period is the window. The flowers open, the adults arrive, eggs are laid, and the next generation begins feeding before the pods harden.The milkweed itself is doing more than hosting one butterfly. Its flowers produce nectar in substantial quantities from structures called horns, small curved projections that hold nectar above the petals. Insects landing on the flowers contact a pollen mass called a pollinium, which adheres to their legs and transfers to the next flower. Milkweed pollination requires a visitor strong enough to pull the pollinium free, which is why larger bees and butterflies are the effective pollinators rather than small flies or beetles. The Taxiles skipper is working these flowers too right now, and the Aphrodite fritillary has been seen on the open slopes nearby. Each visit contributes to seed set, and butterfly milkweed produces its characteristic long, tapered pods through late summer, splitting open in fall to release seeds on silky white fibers.Not everything in this landscape is native. Broad-leaved sweet pea, an invasive plant, is spreading through disturbed areas near the trail edges, and musk thistle, also invasive, has pushed into the open ground between native forbs. Both compete for the dry, open habitat that butterfly milkweed depends on. Neither is a host for the hairstreak. The more these invasive plants establish in rocky, sunny patches, the less suitable ground remains for the milkweed and the butterfly tied to it.The orange of the butterfly milkweed flowers is distinct from almost everything else blooming at this elevation right now. Stand near a plant and give it a few minutes. The hairstreak moves quickly but lands with deliberate stillness, wings folded, green against green.
Showy milkweed awakens its insect allies
May 22, 2026
Along the Colorado Front Range, the first green shoots of showy milkweed (Asclepias speciosa) push through the warming soil. Their leaves unfurl thick and waxy, pale green with prominent white veins that will channel the plant's distinctive white latex. The stems stand barely knee-high now, but each one carries the chemical signature that will draw specific insects across miles of prairie and foothills.Showy milkweed produces compounds called cardenolides in every part of its tissue. These heart toxins make the plant bitter and dangerous to most herbivores, but they also serve as a beacon for the insects that have evolved alongside milkweeds for thousands of generations. The red milkweed beetle (Tetraopes tetrophthalmus) can already sense these young plants. Adults emerge from their winter hiding places in the soil and debris, their bright red bodies marked with four black spots on each wing cover. They climb the tender stems to feed on leaves and mate, completely immune to the toxins that would sicken other insects.The beetles do more than simply tolerate the milkweed's defenses. They concentrate the cardenolides in their own bodies, becoming toxic themselves. Their vivid red coloration advertises this danger to birds and other predators. When the female beetles chew through the stem to lay their eggs inside, they are ensuring their larvae will develop surrounded by the same chemical protection. The plant provides both nursery and armor.Monarch butterflies (Danaus plexippus) will arrive later in the season, drawn by the same chemical signals. The adults sip nectar from the eventual pink flower clusters, but more importantly, the females will deposit their eggs only on milkweed leaves. Monarch caterpillars cannot survive on any other plant. Like the beetles, they sequester the plant's toxins and carry them into adulthood. Their orange and black wings warn predators of the bitter meal they would make.This chemical relationship extends beyond individual survival. When milkweed beetles and monarch caterpillars feed on the plants, they actually stimulate the production of more cardenolides. The plant responds to herbivory by increasing its toxic defenses, which paradoxically benefits the very insects that triggered the response. The beetles and caterpillars become more toxic, better protected from their own predators. The milkweed sacrifices some tissue but gains partners that advertise the danger of eating anything associated with its kind.The timing of these relationships matters as much as the chemistry. Milkweed beetles emerge when the plants are young and the stems are soft enough to penetrate. Monarchs arrive when the plants are mature enough to support caterpillars through their entire development. Each species has calibrated its life cycle to match the plant's seasonal rhythm. The milkweed, in turn, has evolved to be most nutritious and chemically rich when its insect partners need it most.
Beardtongue and the bees of late spring
May 21, 2026
The morning light catches the purple throats of Front Range Beardtongue (Penstemon virens) scattered across the foothills above Boulder. These native wildflowers stand in loose clusters, their tubular blooms opening wide in the warming air. If you are walking these slopes now, you might hear the low hum that signals peak flowering season has arrived.Front Range Beardtongue blooms in late spring when the soil has warmed but before the summer heat sets in. Each flower is a precise tube, deep purple fading to white at the throat, with four stamens tucked inside and one sterile stamen that gives the plant its common name. The bearded tongue. This architecture matters. The tube is exactly the right depth for the native bees that have evolved alongside these plants. Long-tongued bees crawl inside to reach the nectar, picking up pollen on their backs as they work. When they visit the next flower, they carry that pollen with them.But other insects arrive at these blooms too. Seven-spotted Lady Beetles (Coccinella septempunctata), invasive from Europe, climb the flower stalks hunting for aphids and small insects that feed on the beardtongue. These red and black beetles move differently than the bees. They walk across the flower faces, occasionally picking up pollen on their hard wing covers, but they are not efficient pollinators. Their legs are too short, their bodies too smooth. They take what the plant offers without giving much back. The native bees, meanwhile, have branched hairs that trap pollen and bodies shaped by thousands of years of mutual adaptation with plants like this one.The beardtongue depends on this late spring timing. It flowers after the last frost but before the mountain summer drought begins. The plant puts everything into this brief window, producing nectar rich enough to fuel the native bees through their own reproductive season. Leafcutter bees, mason bees, and sweat bees all visit these purple tubes. Each species works the flowers slightly differently, ensuring that pollen moves between plants scattered across the rocky slopes. The beardtongue, in turn, provides protein-rich pollen when few other native flowers are blooming. This exchange sustains both the plant and its pollinators through the narrow corridor of late spring.The invasive lady beetles benefit from this system without contributing to it. They hunt among the flowers, taking advantage of the insect activity the beardtongue attracts. This is how invasive species often establish themselves, not by replacing native relationships but by inserting themselves into existing ones. The beetles do not harm the beardtongue directly, but they do not help it either. They are ecological freeloaders in a system built on reciprocity.
