In our gardens and throughout San Diego County’s diverse habitats, the classic mutually beneficial relationship between the monarch butterfly (Danaus plexippus) and the narrowleaf milkweed (Asclepias fascicularis) thrives.

Narrowleaf milkweed is a key host plant for the monarch, meaning the milkweed plays a pivotal role throughout the butterfly’s life cycle. No other type of plant can substitute. Both the eggs and chrysalises attach to the milkweed’s leaves. During the caterpillar stage, the leaves provide a nutritious food source and also offer protection from predators. How? Milkweed leaves contain cardenolides, which are transferred to the caterpillar and remain in their body into adulthood, imparting a distasteful flavor to predators at both stages. Lastly, milkweed flower nectar is one of many food sources for the adult butterfly.

Chewed milkweed leaves in a garden signal the imminent arrival of the big, beautiful black and orange monarchs! One of the main reasons for monarch decline is pesticide use by farmers and homeowners. To support our local populations, refrain from pesticide use in milkweed habitats.

At the ends of slender, erect stems, pink and lavender-tinted clusters of milkweed flowers attract not only monarchs but also various other nectar-seeking insects. Adult monarchs return the favor by aiding in pollination, essential for milkweed reproduction. If successful, smooth milkweed pods split open to release silky-haired covered seeds, which are dispersed by the wind and hopefully land nearby to propagate as dense clusters of milkweed, preferred by monarch caterpillars.

Even though the timeline between egg and butterfly can be as little as 25 days, welcoming milkweeds into our surroundings can enrich our local ecosystem’s biodiversity throughout the year.